Glossary of Terms
ABECDefinition: Stands for “Annular Bearing Engineering Committee”. When followed by a number (ABEC 5, ABEC 7), it specifies a particular degree of precision. ABEC 1 is standard for most ball bearings, ABEC 3 is precision, ABEC 5 is high precision, and ABEC 7 is extremely high precision. ABEC tolerances are specified to 1/10,000th of an inch, and apply to all tolerances of the bearing.
ABMA (formerly AFBMA)Definition: Stands for “Anti-friction Bearing Manufacturers Association”. The ABMA establishes standards for part numbering and for grades of steel balls, among other things.
AGMADefinition: “American Gear Manufacturers Association”, a global organization representing some 400 companies in the gear industry from over 30 countries. The AGMA takes part in establishing worldwide standards for gear manufacture, and publishes gear manuals, engineering literature, and technical specifications.
Angular Contact Ball Bearing
Definition: A bearing made of several steel balls, held together by a retainer (cage), between two races (inner and outer rings). Internal design is meant to take radial load, as well as moderate axial (thrust) load from one side only.
Options: Can be mounted in sets of two or more, depending on application. Universally flush ground to always mount flush in any combination.
Applications: Some electric motors, vertical hollow-shaft pumps. Most don’t have seals, so must be run in oil and be sealed externally.
How to Order: Part number is easiest. In the absence of a part number, metric dimensions (ID, OD, width).
Definition: Annealing is a way of softening harder metal by heating it to a certain point, holding that temperature for a while, then cooling at a controlled rate. This is often done to setscrew ports. The hardening process can distort the threads and make the metal more brittle. By softening the metal immediately around the setscrew, it becomes less brittle and the distortions are relieved. That way, when the setscrews are tightened (to spec), the threads and surrounding metal will stay intact, rather than cracking and splitting.
Axial (Thrust) Load
Definition: Load transmitted along the axis of a shaft or bearing. Most bearings are designed primarily to take radial load, but can handle axial load equivalent to about ¼ of their rated radial load.
Definition: A bearing made of several balls, held together by a retainer (cage), between two races (inner and outer rings). Some types are meant for higher speeds, some are specialized for higher loads. The vast majority of ball bearings are metric. (“Ball bearing” can also refer to the individual steel balls.)
How to Order: Part number is easiest. In the absence of a part number, dimensions (ID, OD, width). Specify if there are metal shields, rubber seals, a snap ring around the outside, or anything else that appears special.
Definition: An inner or outer ring, on which the rolling elements of a bearing ride.
Options: Configuration depends on the bearing type. In order to last, the races should be made of true 52100 bearing steel, which is hard and wear-resistant. Some manufacturers assume that the outer race of a bearing will be stationary, and the inner race will be rotating, and that therefore the inner race can be made of cheaper carbon steel because the wear will be evenly distributed around the race. However, 52100 bearing steel has a yield strength of 325,000 lbs, whereas carbon steel has a yield strength of only 53,000 lbs (less than 1/6th the strength).
The bearing’s performance depends partly on the smoothness of the rolling path. (It can’t be too smooth, or the rolling elements would skid instead of rolling.) Bearings for wheelbarrows and shopping carts don’t need to be as smooth as bearings for a 3,600 RPM electric motor. Electric-motor-quality bearings usually have ground and honed raceways, for an optimal running surface.
Definition: A bearing component that keeps grease in and keeps most contaminants out. Similar to bearing shield, but with important differences. Seal is fixed to outer race, and has light or moderate contact with inner race. Therefore, it generates very slight drag, which is usually a non-factor at most speeds, but can create heat at very high speeds. More effective at keeping contaminants out than a shield.
Options: Most bearings use standard seals that make moderate contact with inner race. Where drag is a concern but contaminants are also a concern, some manufacturers offer “light-contact” or “non-contact” seals, which allow the bearing to run at higher speeds than normal seals without generating as much heat.
On mounted bearings, seal may be protected by a flinger.
Seal material is normally nitrile rubber (good up to about 225 degrees), but in high-temperature or some automotive applications, Viton® (good up to about 400 degrees) may be available. Teflon® seals also on some specialized bearings. However, these are both special options and are not usually readily available.
Applications: Where good protection is needed at low-to-moderate speeds. (The speed limit at which shields vs. seals matter depends on the size of the bearing.) Good for outdoors or other applications exposed to moisture or splashing. Also better than shields for keeping out very fine contaminants.
Definition: A bearing component that keeps grease in and keeps most contaminants out. Similar to bearing seal, but with important differences. Shield is fixed to the outer race, and comes close to the inner race without actually touching its surface. Therefore, it generates no drag and allows higher speeds than a seal. However, since there is the slightest space between the shield and the inner race, it does not keep out very small contaminants.
Applications: Where moderate protection is needed at high speeds. (The speed limit at which shields vs. seals matter depends on the size of the bearing.) Often used in routers or other small, high-speed hand tools. Since shields tend to be slightly less expensive than seals, they are also used in high-production items for low-speed, low-contaminant environments, such as ceiling fans, vacuum cleaner wheels, etc.
Definition: A plain bearing made of bronze alloy, for low-speed applications.
Options: Solid bronze bushings are machined and finished from cast bronze bar stock, such as SAE660. Since they are solid, they depend on external lubrication; even though solid bronze alone has greater strength than sintered bronze, it will wear out quickly with no lubrication. Some have grooves (either empty or filled with solid lubricant) to allow lubrication to reach all running surfaces.
Sintered bronze (sometimes called powdered bronze) bushings are made of bronze alloyed with other metals. The component metals are ground to a powder, then heated to the point where everything but the copper melts, then cooled into a porous bushing and vacuum-impregnated with oil. Though physically weaker than solid bronze, the integral lubricant helps it to last longer than un-lubricated solid bronze. Sintered bronze bushings are available with or without a flange on one end, and are usually a few thousandths oversized on the ID and the OD, to allow for a press-fit and for proper running clearance.
Applications: Low-speed, low-load, low-profile applications. Exercise equipment, upper strut hinges in automobiles, gates, and the like. Exposure to dust or to porous contaminants (like sawdust) will wick the oil out of the bushing, so it should be protected or enclosed.
How to Order: Specify solid bronze (usually smooth and shiny) or sintered (powdery appearance). Dimensions (ID, OD, width), and if sintered, whether there is a flange at one end.
Definition: A single piece of material that performs the function of a bearing.
Options: Available in solid or oil-impregnated bronze, also some low-friction plastics. Some can run lube-free, others require oil or grease.
Applications: Good for low speeds and low profile. Hinges, some wheels, shock absorbers, many back-and-forth (as opposed to continuous rotation) joints.
Bushing (shaft mounting)
Definition: A component that goes between a shaft and another component (sprocket, sheave, etc.), for the purpose of locking that component to the shaft. Typically tapered on the outer diameter, with provisions for bolts or screws to secure the bushing to the outer component; as the bolts or screws are tightened, the bushing is drawn further into the outer component, and the taper causes the inner diameter of the bushing to compress around the shaft.
Options: Three principal styles are common in the industry: “taper-lock”, non-flanged with half-holes (which correspond to half-holes on the outer component) for locking; “QD”® (for “Quick Disconnect”) and “split taper”, both flanged styles with mounting bolt holes through the flange, and with or without keyways on the outer taper for additional locking power.
Applications: Available in very small sizes, but most common for sprockets and sheaves larger than 4-5”. Also used on conveyor belt pulleys.
How to Order: Part number is easiest. If no part number on the bushing, it may be indicated by a portion of the part number on the mounted component. If not, specify shaft size, OD, flange thickness, bolt circle, and OD of taper just behind flange.
Cam Follower / Yoke RollerDefinition: A needle roller bearing with a thick inner race and outer race. Cam followers have their own threaded stud sticking out one side, and usually have a grease provision via the stud or the outer face. Designed primarily for radial load, may or may not be able to handle minor axial (thrust) load. Options: Regular or heavy stud; eccentric sleeve on bearing end of stud to allow adjustment without drilling new holes in mounting surface. Applications: Good for rolling-track applications. Bearing can be mounted in the moving component, or can be stationary to support something moving on top of it. How to Order: Part number if possible; otherwise, roller OD, stud diameter (or hole diameter if yoke roller), and roller width.
Centerless GrindingDefinition: A type of machining used to create precision cylindrical parts. Rather than securing the part on a center, as might be done with a lathe, the part is put in between a regulating wheel (which makes it turn) and the grinding wheel. It allows dimensions to be held very accurately and creates a clean, smooth surface.
ChainDefinition: A long strand of interlocking links (usually of metal), for power transmission or for conveying material. Driven by sprockets. Options: Variety of pitches (link lengths), styles (roller chain, pintle chain, mill chain, engineering-class chain, drag chain); selection depends on application demands. Wide assortment of link attachments can be used to convey material. Some chains have features that will contribute to longer life than other similar chains. Applications: Roller chain is usually preferred for power transmission. Chain with certain attachments can be used to convey material (like wood in a mill). Performance ratings are based on lubricated operation, so ideally the application should take this into account. How to Order: Number may be on sideplate. If not, measure from center of one pin to center of neighboring pin, roller diameter, and pin length. (See also chain-related questions in our FAQ.)
Definition: The amount of space between the rolling elements and the races of a bearing. Some space is necessary to allow grease or oil to get between them. A natural consequence of internal clearance is a slight amount of “play”, or movement of the races in relation to each other. Clearance is specified by numbers like C2, C3, C4, and such; each C number corresponds to a minimum and maximum clearance, and each C number’s range overlaps the next range up and down. Clearance is not to be confused with precision or with quality.
Options / Applications: The clearance needed is determined by the nature of the application. Most electric motor bearings are C3 clearance. A heavy-duty machine like a shaker screen requires the bearings to be very tightly installed, which will lead to a loss of some of the bearing’s clearance. Therefore, some bearings are made with greater initial clearance (C4) so that they can be heavy-press-fit without losing all their clearance once installed. Other machines require minimal “play”, and so specify a C2 clearance.
Conrad BearingDefinition: A bearing made of several balls, held together by a retainer (cage), between two races (inner and outer rings). Internal design is meant to take radial load, as well as light axial (thrust) load from either side. Options: Single-row or double-row (wider). Snap ring on the outside; metal shields or rubber seals to keep grease in and dirt/water out. Applications: Everything from drills and routers to cars and high-speed electric motors. Good balance of speed and load capabilities. How to Order: Part number is easiest. In the absence of a part number, dimensions (ID, OD, width). Specify if there are metal shields, rubber seals, a snap ring around the outside, or anything else that appears special.
Definition: A device used to positively mate one shaft to another shaft, or to mate a shaft to a flywheel.
Options: Can be a simple rigid sleeve to lock two shafts together, or can be a larger set of two metal hubs with a central element (various materials available). Selection criteria are speed, horsepower, and dampening / misalignment required.
Applications: Anywhere two shafts meet end-to-end and need to turn at the same speed. Found between some motors and gear reducers, also on large mowers, pump shafts, and the like.
How to Order: Part number if possible. If not, many styles are available, and within a style there may be various sizes that fit the same shaft; therefore, size will be based on shaft size, horsepower, and speed.
Cylindrical Roller Bearing
Options: Races may have shoulders or retaining rings to allow for removal or disassembly, and to accept some axial (thrust) load in one direction.
Applications: Large electric motors. Most don’t have seals, so must be run in oil and be sealed externally.
How to Order: Part number if possible. If not, dimensions (ID, OD, width), which are usually metric. Specify which race(s) are shouldered and on which side(s).
Eccentric Locking Collar
Definition: A bearing inner race may be extended out one side, and have a shoulder machined onto the outer surface. This shoulder is circular, but deliberately slightly off-center. The collar has a matching off-center shoulder machined into one face. During installation, the collar slips over the shoulder of the inner race, and then is twisted in the same direction as the shaft will rotate. As it is twisted and the shoulder circles move out of alignment with each other, the collar is forced against the shaft in one direction, and the race in the other direction. This results in a squeeze fit on the shaft.
Options: Since each manufacturer can determine the size and degree of eccentricity of their machined shoulders, you can’t necessarily mix-and-match one brand’s collar and another brand’s bearing. (Most manufacturers sell the collars with the bearings, so you don’t usually need to worry about this.) If you want to buy a spare collar or replace an existing one, you certainly can – but nobody can guarantee that the collar will fit the bearing unless they’re both from the same manufacturer.
Applications: Suitable for many relatively low-speed applications, or where exceptional balance isn’t an issue. Great for slow-moving axles, sprocket or sheave support bearings, and the like. Since the tightness depends on the direction of shaft rotation, this may not be a good option for reversing shafts.
Definition: Although metal is hard, it deforms ever so slightly when it’s under load. Depending on time and the load, it usually springs back to its former shape immediately; however, after a large number of load-unload cycles, it loses its ability to spring back, and the deformation becomes permanent.Fatigue life of metal can be extended by additional hardening, by selecting the appropriate grease, and by eliminating factors like vibration and misalignment that can accelerate wear. The process used in making a bearing race can also contribute to long life: forged rings have a unified grain structure that helps resist fatigue.
Definition: Mounted bearing that supports a shaft perpendicular to the mounting surface. (If a flange block were bolted to the table in front of you, the shaft would be vertical.)
Options: Two-bolt diamond-shaped housing or four-bolt square housing are the most common. Some have two holes very close to the insert, or three holes off on one side (chevron-shaped).
Applications: Supporting long shafts that run through mounting surface. Can be used on either side of fans, or to support sprockets or sheaves.
How to Order: Part number is a combination of the bearing number and the housing number; therefore, specify both of those numbers if possible. If not, specify shaft size, 2- or 4-bolt, bolt spacing, and locking style (setscrew or eccentric collar).
Definition: A metal plate, fixed to the extended inner ring of a bearing just outside the bearing seal. Flinger rotates at same speed as shaft, providing a solid, spinning barrier to keep contaminants away from the seal.
Applications: Commonly found in mounted bearings with extended inner ring. Good for keeping heavy contaminants away from the more fragile rubber seal.
Definition: As noted under ABEC, bearings can be made to differing degrees of precision. But if you stack multiple bearings together, the individual variations in precision could add up to important differences in the overall length of your stacked assembly. So for bearings that tend to be used in sets, such as angular contact ball bearings, not only does each bearing need to be within a certain tolerance of the nominal dimensions, but each bearing must be within a certain tolerance of its neighboring bearings. Otherwise, a stack of bearings could be 1/1000th of an inch too long or too short, which could be crucial in precision equipment such as a lathe or planer.To make sure that the stacks of bearings can hold the same tolerance as any single bearing, the mating faces of the bearings are “flush ground” to an exceptional smoothness. In past years, bearings were flush ground in matched sets. Nowadays, bearings are “universally flush ground”, so that any flush ground bearing can be installed right up against any other flush ground bearing, with no significant variations between them.
Food Grade Bearings
Definition: A mounted bearing specifically designed for use in food-related applications. This bearing must be different from standard units because it will likely be washed down regularly, and must meet industry standards for being in the proximity of food.
Options: Various materials (plastics or stainless steel) that resist corrosion. Stainless steel is the most durable material, but many manufacturers use plastics because they’re cheaper. Food-grade grease approved for “incidental contact” with food items. Since bacteria can grow in crevices, these are usually smooth bearings with few or no places where a washdown can’t reach.
Applications: Anything from cheese making to fruit preparation. Because of corrosion resistance, these bearings can be used in car washes and similar applications.
Definition: The least expensive way to make a bearing ring would be to cut it from a hollow roll of steel and machine it. Some bearing manufacturers make rings this way as a cost-cutting measure. However, steel has a grain structure just like wood does, and rolled steel can have the grains aligned any which way.Forging involves pouring the molten steel into a mold and introducing the die into the middle of the mold; as this forces the liquid metal to the outside of the mold, it makes the grain structure align in in the direction of rotation, rather than across the rolling path. This is a more expensive and time-consuming process, but the aligned grain structure helps the steel to retain its shape under load.
Definition: A toothed wheel for use in direct interface with another gear. Not to be confused with a sprocket, which is for use with chain. When ordering, the most accurate method is to know the number of teeth, the width of the gear face, and the pitch (teeth per inch).
Options: A variety of shapes and types: worms and worm gears, for high-reduction drives; helical gears, such as are in car transmissions; spur gears and gear rack, with teeth straight across the gear face; miter and bevel gears, with matching angled faces. Assortment of pitches depending on speed and power needed. Most are metal (steel, cast iron, bronze), a few are available in plastic materials.
Applications: Gear reducers, some hand-powered machinery.
How to Order: Most accurate way is number of teeth and outer diameter. Specify which type (see “Options”) and bore size.
Definition: Commonly called “gearbox”, an enclosed transmission using gears to convert a specific input speed to a higher or lower output speed. Since electric motors turn around 1,200, 1,800, or 3,600 RPM, gear reducers are often used to reduce that speed down to the desired level.
Options: Variety of internal gears, such as worm, helical, planetary, etc. Worm gear reducers can accomplish high ratios, but can be inefficient (less than 70%) due to amount of friction generated. Helical gear reducers are much more efficient (up to 97%) in the same space.
Besides gears themselves, the input/output shafts of a gear reducer may be inline (sharing a common axis), parallel (but not inline), or at right angles to each other. Housing may be roughly square and bolt onto surface, and have mounting flange for electric motor or have solid input shaft for other input options. May be “shaft-mount”, with hollow input and output, and come with accessories to hang from common frame with motor.
Applications: Where space and/or power requirements rule out long-center drives. Shaft-mount reducers are common in conveyor applications.
How to Order: If replacing an existing reducer, start with that part number. If starting from scratch, specify input speed and horsepower, desired ratio or output speed, and any mounting constraints.
Definition: Grease is basically a molecular sponge for holding oil inside of a bearing and near the load surfaces. As a rolling element passes along the raceway surface and grease is forced between the two, the grease compresses and releases a film of oil, then soaks it back up once the element has passed. Grease also helps dissipate some of the heat away from the load surfaces of the rolling elements.
Options: Greases are made of various base materials – some are approved for use near food, others perform better in various temperature ranges. Different greases handle loads differently, depending on how much load they’re designed to take before breaking down. Not all greases are compatible with each other; before greasing a bearing that has previously had grease in it, you should check to make sure that the greases won’t break each other down.
Definition: Since gears have to transmit a lot of power in a small amount of space, their efficiency depends on the smoothness of the surfaces where the teeth meet. Some manufacturers only shave or roll their gearing, since these are faster and cheaper processes. However, shaving is limited by the hardness of the gear material, and in rolling, small slivers or lips of metal can be rolled over the edges. Grinding the tooth surface takes longer and costs more, but it produces a smoother finish; this, in turn, allows the same size gear to transmit more horsepower and to run cooler, more smoothly, and more quietly.
Definition: Unit of steel or of cast iron, with a specially machined opening to accept an insert. Allows easy mounting of a bearing to just about any surface. Any housing style can be used in combination with any other housing style as long as there’s a surface to mount each one to.
Options: For variations on the mounted bearing, see pillow block, flange block, and take-up unit. The most common bearing insert is a ball bearing. For large-diameter shafts, a housing may be split (and bolt together) to allow for use of a large spherical roller bearing.
Definition: Radial ball bearing that is specifically designed for use in a mounted bearing. Follow the same general size series as regular metric ball bearings, but usually have inch-size bores. Outer race is usually spherical; bearing is inserted into housing at 90 degrees, then rotated into place.
Options/features: Locking to the shaft by setscrews in the inner race, by an eccentric locking collar, or by a tapered adapter sleeve. Inner race extended out of one or both sides. Some are greaseable, others are “lubed for life” (not greaseable). Steel flinger outside the seal to protect it from dirt and contaminants. Most have small pin on outer diameter that fits into an open space inside the housing, and prevents the outer race from spinning in the housing during operation. A few inserts have cylindrical outer races, and some have an outer race snap ring.
Definition: The “International Organization for Standardization”, a body that sets industry and commercial standards and specifications worldwide, for everything from construction and security and quality control to bearings and chains. Its members are representatives from various national standards organizations from over 150 countries.Power transmission products must meet or exceed ISO standards for dimensional accuracy, precision, tolerances, load requirements, etc. Most manufacturers base their catalog information (including load and life information) on ISO-developed formulas.
Keyless Locking Device
Definition: A device that performs the same function as a bushing, but by pure pressure, without requiring mechanical engagement to either the shaft or outer component. A keyway actually reduces the torque capacity of a shaft, and can wear out over time. A keyless locking device is made of 2-4 pieces with internal tapers, and integral adjusting bolts, so that its outer diameter expands and its inner diameter contracts when the bolts are tightened. Thus, it rigidly fixes the outer component to the shaft without weakening the structure of either. A keyless locking device has greater torque capacity than the shaft itself, so it will not slip.
Options: Balance of torque and space requirements; some are lower-profile, some are heavier for higher torque. Most are self-centering. Most have several adjusting bolts, smaller ones have a single large nut.
Applications: Can be used anywhere that a bushing can be used, but is cylindrical rather than tapered. Transmits very high torque compared to size, so good for high-torque, high-speed machinery. Great for timed applications, since there’s no slip.
How to Order: Start with shaft size, horsepower, and the hub OD of the mounted component.
Definition: Also known as the “L10 life”, this is a theoretical number, based on the number and size of the rolling elements, the thickness of the races, and a particular range of speeds and loads. This number does not represent how long one specific bearing will actually last; rather, this is how long approximately 10% of a group of identical bearings will last, under a given load and under perfect conditions. (That means that about 1 bearing in 10 will fail before this point; your average bearing will last 5x this long; and some bearings will last 10x as long.)
Definition: A bearing that is designed for linear movement along a rail or shaft, rather than rotation. Bearing elements are held inside some sort of block, and either the rail or block is stationary while the other part moves back and forth.
Options: Balls or rollers, or low-friction plastics for the bearing surfaces. A nearly endless array of block and rail arrangements, depending on the demands of the application. There is no single “bread-and-butter” linear bearing, they are all designed for a specific type of use. Since there are so many options, most linear bearing assemblies are ordered-as-needed, and most technical engineering is best done by the customer and the manufacturing engineers, rather than the distributor.
Applications: Anything requiring back-and-forth motion. Environment must be fairly clean, since seals heavy enough to exclude most contaminants would also generate a lot of drag and reduce the machine’s efficiency. Low-friction plastics may be better for outdoor applications.
Definition: This is a theoretical number, based on the number and size of rolling elements, the thickness of the races, and a specific life calculation or number of revolutions. Load ratings are separated into “dynamic” (running) load and “static” (ultimate capacity when not running) load. Read the fine print when figuring out a load rating: a 35,000-lb rating may be impressive, but it’s probably based on only 500 hours at 33 RPM. Choose a bearing that can handle the load you want for the life expectancy you want.
Definition: Usually a radial ball bearing, sometimes a roller bearing, held within a housing (normally cast iron or steel). The bearing inside is known as an insert, and has a rounded outer diameter that allows it to be removed and installed by hand, but holds it inside the housing during operation. Various housing styles allow for different mounting arrangements. Part numbers are usually a combination of the number on the housing and the number on the insert.
Options: Locking to the shaft by setscrews in the inner race, by an eccentric locking collar, or by a tapered adapter sleeve. Housings can be 2- or 4-bolt pillow block or tapped-base pillow block; 2- or 4-bolt square flange block or piloted round flange cartridge; also conveyor take-up units, a few other variations. For large-diameter shafts, a mounted bearing may have a split housing and use a spherical roller bearing.
Applications: Usually used in pairs; due to the way the inserts fit inside, one bearing alone normally can’t hold a shaft straight. Fans, mixers, car washes, anywhere there’s a long shaft that needs support.
How to Order: See “How to Order” under the style in question (follow link from “Options).
Needle Roller Bearing
Definition: A bearing made of several needle rollers. Outer race may be a thin shell or a thicker sleeve. Some run on inner races, can also run on a hardened steel shaft. Designed for radial load, usually not meant for axial (thrust) load. A variation is the cam follower or yoke roller.
Options: With cage or without (full complement). Rubber seals may be available.
Applications: Alternators, some automotive clutch pilot bearings. High load capacity in a low-profile bearing at moderate speeds.
How to Order: Part number if possible; if not, specify ID, OD, width. Does it have an inner ring (which will be a separate part), or does it ride directly on the shaft?
Definition: A device to keep lubricant inside of a part and to keep contaminants out. Most common design has a steel body and a spring-loaded rubber lip; older styles used leather and felt for lip materials.
Options: The critical lip is the spring-loaded lip, which keeps grease or oil inside of your part. Some seals are double-lip; the second lip does not keep grease in, but is lighter than the primary lip and is angled against the shaft to keep dirt and water from getting to the primary lip. Most oil seals are nitrile rubber (rated up to about 225 degrees), Viton® also available (rated up to about 350 degrees).
How to Order: Part number if possible, since many can be interchanged. If no part number, or if not interchangeable, specify actual shaft size (not seal ID), seal OD, and width.
Definition: Mounted bearing that supports a shaft parallel to the mounting surface. (If a pillow block were bolted to the table in front of you, the shaft would be horizontal.)
Options: Two-bolt is most common, though some larger units have four bolt holes (two in each foot). Some have no feet, but have threaded holes coming up from the bottom, called “tapped base”.
Applications: Supporting long shafts that run parallel to a surface. Can be used on either side of squirrel cage fans, or to support sprockets or sheaves.
How to Order: Part number is a combination of the bearing number and the housing number; therefore, specify both of those numbers if possible. If not, specify shaft size, bolt spacing, and locking style (setscrew or eccentric collar).
Definition: Chain made of U-shaped links, where the pin at the open end of one link goes through holes at the closed end of the next. Not to be confused or interchanged with roller chain; pintle chain is for much slower and nastier applications, and runs on completely different sprockets.
Options: Heat-treated components contribute to consistent performance. Quad-staking the pin ends increases holding power.
Applications: Few moving parts make it ideal for applications with heavy corrosion or contamination, such as in fertilizer spreaders, abrasive conveying, and the like. Links scoop contaminants out of the sprocket root, and there is space between the pin and the barrel of the link to let contaminants out; this helps avoid tension due to material build-up.
How to Order: Number may be on sideplate. If not, start by measuring from center of one pin to center of neighboring pin.
Definition: The distance between a central point on adjacent links (chain) or teeth (sprockets, gears, synchronous drives). Ratio and diameter calculations based on pitch are more accurate than using outer diameters.
Options: On gears and sprockets, pitch diameter is located partway down the tooth, and represents the line of greatest contact, at which the most power is transmitted. “Diametral pitch” (gears) is the number of teeth per inch of circular diameter; a 16 pitch gear will have 16 teeth per inch. “Circular pitch” (sprockets) is the distance between adjacent pitch points (the center of where the chain roller should ride between the teeth), measured on the pitch circle and usually in graduations of 1/8″ or 1/4″. On V-belt drives, “pitch diameter” refers to the diameter of the sheave where the power-transmitting cords actually run, which is usually a bit below the outer diameter of the belt.
Definition: A process of machining a shaft to a specific measurement. Some grinding processes work from one end of a part to the other, creating the slightest spiral groove pattern on a shaft, which could cause oil to leak past a sealing surface. Plunge grinding is a form of centerless grinding; the grinding wheel comes straight into contact with the part, and comes straight off the surface when done. This is the preferred process for seal surfaces, since it doesn’t make a spiral pattern.
Definition: A nearly flat belt with several small V-shaped ribs on underside. In cars, often called a “serpentine belt”. When ordering, the number of ribs and the total width of the belt will be needed.
Options: Some flexibility in number and size of ribs (and therefore in width).
Applications: Good for transmitting moderate amount of horsepower in low profile. Seen in cars as alternator belt or as entire serpentine belt (however, the rib size used in most cars is only available from auto parts stores). Also seen in some saws or sanders.
How to Order: Part number may be helpful, but sometimes not interchangeable or incomplete. If insufficient, specify length, number of ribs, and overall width. J (3/32″), L (3/16″), and M (3/8″) ribs are industrial belts; K ribs are automotive only, and must be purchased from an auto parts store.
Radial LoadDefinition: Load transmitted at 90 degrees from the axis of a shaft or bearing. (If you were holding the shaft horizontally in both hands, radial load would be directly down on the shaft.) Most bearings are designed primarily to take radial load.
Definition: A device that holds rolling elements within a certain distance of each other, and keeps them from falling out of the bearing.
Options: Materials can vary widely, from plastic to fiberglass to bronze to steel. Plastic is the cheapest to manufacture, and is used by many bearing makers as a cost-cutting measure; however, plastic is the weakest material and typically does not respond well to heat. Steel is usually the preferred material in ball bearing retainers, since it is the most rigid and heat-resistant. In roller bearings, steel and bronze tend to be preferred, particularly since bronze excels at dissipating heat away from the rolling elements. Some manufacturers used to make bronze or steel cages as a standard, but switched to cheaper materials and now offer bronze or steel cages as “premium” features for an extra fee.
Definition: A bearing made of several rollers, which may be cylindrical, needle, spherical (rounded like barrels), or tapered. (Not the same as ball bearings.) Rollers are usually held together by a retainer (cage), between two races (inner and outer rings). Capabilities depend on style.
Options / Applications: Needle roller bearings are good for high load capacities in a relatively small space. Cylindrical roller bearings have high load capacities, but usually cannot handle axial (thrust) load. Spherical roller bearings have high load capacities, can handle axial (thrust) load, and can take high speeds. Tapered roller bearings are in many automotive wheels.
Definition: Articulating chain that transmits power between two (or more) sprockets.
Options: Some variations in the width or thickness of sideplates, can help increase load capacity. Most standard chain has split bushings and some have split rollers (rolled from a flat piece of metal); use of solid bushings and solid rollers can improve performance. To retain lubricant where it’s needed most, some chains feature an oil reservoir hole in the bushing. Pins can be quad-staked for better holding power on the plates.
Applications: Good for transmitting high horsepower at low to intermittent speeds. Found on anything from bicycles to lawnmowers to lumber mill equipment. Chain with oil reservoir can be used in wood applications where sawdust tends to soak up oil near the chain surfaces.
How to Order: Number may be on sideplate. If not, measure from center of one pin to center of neighboring pin, roller diameter, and pin length.
(See also chain- and sprocket-related questions in our FAQ.)
Setscrew Locking (Bearings)
Definition: A bearing inner race may be extended out one side, and have two setscrews installed. Since many shafts tend to be a little bit undersized, setscrews are an economical way to secure the bearing to the shaft. Rather than coming to a sharp point, most setscrews end in a small hollow hexagon, which lets each screw tighten against more shaft area than a point would allow.
Options: Different manufacturers place the setscrews at various places (60, 90, or 120 degrees apart). These make some difference in the holding power vs. the centering ability of the bearing.Alternate locking devices are eccentric locking collar or tapered adapter sleeve.
Applications: Suitable for many relatively low-speed applications, or where exceptional balance isn’t an issue. Great for slow-moving axles, sprocket or sheave support bearings, and the like. Since the tightness does not depend on the direction of rotation, this is a good option for reversing shafts.
Definition: A grooved wheel for use with a belt (or belts). Sometimes called a “pulley”, but “pulley” is a broader term that refers to a variety of very different parts. Sheaves are typically used with single or multiple V-belts, or with smaller poly-V belts. When ordering, the most accurate method (if part number is not known) is to specify the belt section and the pulley outer diameter; wrapping a rope or string around the pulleys is not accurate.
Options: Various groove profiles and widths to match industry standard belts. Smaller sizes can lock directly to shaft with key and setscrews; most larger sizes require some type of bushing.
Applications: Good for higher speeds than a chain drive. Typically used in HVAC equipment.
How to Order: Part number is easiest. If not, specify belt section (4L, 5L, A, B, C, D, 3V, 5V, etc.), number of belts, and sheave OD (not groove-bottom diameter). Also specify mounting method: if straight bore, specify bore size; if tapered bore surrounded by holes, measure large taper ID and bolt center.
Spherical Roller Bearing
Definition: A bearing made of several spherical rollers, held together by a retainer (cage), between two races (inner and outer rings). Can take high radial load as well as axial (thrust) load, at higher speeds than cylindrical roller bearings.
Options: Double-row is standard, single-row is also available. Lubrication groove and holes on outer race also standard. Single-row can be supplied with seals, double-row usually open (and therefore must be run in oil and sealed externally). Larger internal clearance available for heavy press-fit applications, like shaker screens. Can be supplied with a tapered bore, for mounting on a tapered shaft or using a tapered adapter sleeve. Various retainer materials and styles.
Applications: Large electric motors. Can be mounted in split bearing housings for long heavy shafts.
How to Order: Part number if possible; if not, bearing dimensions (ID, OD, width), almost universally metric. Specify whether bore is tapered or straight, and mention the application, as some require greater internal clearance than others.
SprocketDefinition: A toothed wheel for use with chain. Not to be confused with a gear, which is for use in direct interface with another gear. Options: With or without hub. Can be fixed to shaft with integral setscrews, or use a variety of bushings. Selection of pitches to match all sorts of chain; most common sprocket type is for use with roller chain. Applications: Good for transmitting high horsepower at low to intermittent speeds. Found on anything from bicycles to lawnmowers to lumber mill equipment. Two sprockets can accomplish up to a 7:1 ratio; any greater ratio should use two or more reductions of up to 7:1 each. How to Order: In the absence of a part number, the most accurate method is to specify the pitch and the number of teeth. The pitch may be indicated by a number on the sideplate of the chain, or can be estimated by measuring from tooth to tooth. Also specify mounting method: if straight bore, specify bore size; if tapered bore surrounded by holes, measure large taper ID and bolt center. (See also chain- and sprocket-related questions in our FAQ.)
Definition: The individual balls that are used in the manufacture of bearings. Many bearing distributors also sell individual steel balls. This does not mean that ball bearings can be rebuilt; most bearing manufacturers do not specify which size balls they use, and disassembly of the bearing to get the balls out will likely damage other components beyond repair.
Options: Steel balls are commonly available in many fractional-inch sizes, as well as a few metric sizes. Steel balls are made in various “grades”, or tolerances. Since it’s physically impossible to make a perfectly round ball, the grades specify how out-of-round a ball is allowed to be. Grades specify the tolerance in millionths of an inch, so the smaller the Grade number, the more precise the ball is. A Grade 1000 ball can be 0.001000” out of round, whereas a Grade 25 ball can only be 0.000025” out of round.
How to Order: Since “ball bearing” usually means an assembled bearing, ask for “steel balls”. Specify diameter; most common are fractions of an inch, though there are a few easily-available metric sizes.
Definition: A toothed belt for use with a synchronous pulley. Commonly referred to as a “timing belt”. Inch series have trapezoidal teeth and are true timing belts, whereas metric series have rounded teeth and are more accurately called “HTD belts” (HTD is for High-Torque Drive).
Options: Inch or metric, various pitches and widths, as well as some stiffer belt and cord materials; all dependent on the horsepower required and the space available.
Applications: Transmits more horsepower than a V-belt drive in the same space, and quieter (and can run faster) than a chain drive in the same space. Used in timing / indexing applications, since there is no slip between belt and pulleys. Ranges from very small belts (inside of copying machines) to automotive timing belts to much larger and wider belts.
How to Order: Length, width, and pitch (distance from tooth tip to tooth tip). May need to specify tooth shape (rounded or trapezoidal). Note that at the small end of the pitch range, there is a 5mm pitch and a 1/5 inch pitch, which are very similar; in that case, measure the length of ten teeth (from tip to tip). Either all measurements will be in fraction-of-an-inch increments, or all will be in whole millimeters.
Definition: A toothed pulley for use with a synchronous belt. Similar in appearance to a gear, but not made to interface with another pulley directly. Also called “timing pulley” or “HTD pulley”, depending on which kind of belt it uses.
Applications: Same as synchronous belt.
How to Order: Number of teeth, distance from tooth to tooth, and face width (between flanges if there are any). Note that at the small end of the pitch range, there is a 5mm pitch and a 1/5 inch pitch, which are very similar; in that case, measure the length of ten teeth (from tip to tip). Either all measurements will be in fraction-of-an-inch increments, or all will be in whole millimeters. Also specify mounting method: if straight bore, specify bore size; if tapered bore surrounded by holes, measure large taper ID and bolt center.
Definition: Mounted bearing with slots on either side and a single hole for an adjustment bolt, to be used in conjunction with a take-up frame.
Options: Wide or narrow slots, depending on the frame being used.
Applications: Used in pairs to support a conveyor pulley between them, and allow the position of the pulley to be adjusted by means of the bolt.
How to Order: Part number is a combination of the bearing number and the housing number; therefore, specify both of those numbers if possible. If not, specify shaft size and locking style (setscrew or eccentric collar). Usually two slot widths are possible, so measure the inside width of the side slots also.
Tapered Adapter Sleeve
Definition: A sleeve, often accompanied by a locknut and lockwasher, that is used to lock a tapered-bore bearing onto a shaft. The sleeve may have a slot at the narrow end, where the washer has a tang that slips into the slot, and the nut threads on behind it. As the nut is tightened, it draws the tapered sleeve into the bearing bore, and the sleeve clamps down on the shaft. Once installed, tangs on the outside of the washer can be bent into small notches in the nut to prevent it from loosening.
Options: Metric or inch threads may be available (must match the nut threads), but the threads do not necessarily make the sleeve diameter inch or metric. Most regular ball bearings are not tapered-bore; this mounting system is far more common in mounted ball or roller bearings, especially spherical roller bearings. When it is used in a mounted ball bearing, it requires a larger bearing for the same size shaft as a straight-bore; spherical roller bearings do not need to be upsized.
Applications: Other locking devices may result in a slightly crooked fit, which can reduce the life of a bearing by up to 66%. A tapered adapter sleeve fits and runs true, which means the bearing will last longer. This can make a big difference in large fan applications (where balancing is critical), or any application where a shaft needs to run exceptionally true.
How to Order: Specify inside diameter and length; if possible, include part number or measurements from the nut or washer, as various sized sleeves may fit the same shaft.
Tapered Roller Bearing
Definition: A bearing made of several tapered rollers, held together by a retainer (cage), between two races (inner and outer rings). The rollers and cage are usually assembled to the inner race, and are known as the “cone”. The outer race is usually separate, and is known as a “cup”. In the inch bearings, cups and cones can be mixed and matched within small series. In the metric bearings, a single bearing number specifies the cup and cone, and these should not be mixed and matched with others. Cups and cones should not be mixed between manufacturers.
Options: Some versatility in size combinations; a dozen or so cups will fit a dozen or so cones, allowing a measure of freedom in selecting your shaft and housing size. However, since the size and shape of the rollers, as well as the angle of the races, changes from one series to the next, you should make sure that you only combine bearings from the same series. A very few bearings are available with one seal.
Applications: Primarily automotive, such as in car and trailer wheels.
How to Order: Part number is definitely preferable, since bearings of similar sizes can have different internal geometry. If replacing an existing bearing, shaft OD and housing ID are best bet. If starting from scratch, bear in mind that not every possible combination of ID and OD is actually available; specify the most critical dimension and we’ll work with it from there.
Options: Most common are needle roller or ball type; also available in cylindrical roller or tapered roller.
Applications: Anytime the load is transmitted along the length of a shaft, rather than against it.
How to Order: Specify shaft size, acceptable OD, and bearing thickness.
Definition: A belt with a trapezoidal cross-section meant for use in a sheave. Belt is mostly rubber, but has cords running the length that transmit the power. When ordering without a part number, the width and outside length are usually sufficient; if the same width is used on more than one profile, the height of the belt may also be needed.
Options: Different profiles and widths, must be used with sheave meant for the same profile and width (can’t necessarily be mixed-and-matched). Most are smooth and fabric-wrapped for quiet running, some are cogged (small notches cut out from underside) and non-wrapped for heat dissipation and higher horsepower. Multiple belts can be run on a multiple-groove sheave to increase power capacity. Some options in cord material can give the belt more power.
Applications: Good for moderate loads at moderate speeds (higher speed than chain drive). Requires no lubrication, just occasional tensioning to maintain efficiency.
How to Order: Start with any numbers on the belt. If they don’t interchange, specify outside (not inside) length), the back width of the belt, and any numbers off of your sheave. Some widths (such as 5/8″) are available in more than one profile and can’t be mixed, so belt height may also be needed.