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Basics of... Bearings


The typical functions of a bearing are to allow shaft rotation while minimizing frictional losses and/or supporting the shaft and its associated loads. Bearings are typically selected based on a required life in hours. Life is directly affected by the load applied to the bearing and the rotational speed of the bearing.



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Common Terms

Ball: Creates a point contact between the ball and ball path with the rolling element, distributing loads across a small area. Surface contact is minimized and less friction and heat is generated. This gives ball bearings a higher speed range but lower load capability.

Tapered Roller: Distributes loads across a larger area by creating a line contact between the raceway and rolling element. A double row provides twice as many rolling elements available to carry bearing loads. This increases bearing radial load capacity but reduces speed capability. Tapered roller bearings can accept heavy loads from both the radial and thrust directions.

Static Misalignment: A fixed misalignment, such as uneven mounting surfaces between two bearings. Both ball and tapered roller bearings have very limited internal misalignment capabilities. However, some mounted ball and mounted tapered roller bearings have some static self-aligning capability between the housing and bearing inserts.

Dynamic Misalignment: Occurs due to a constantly changing angle of alignment, such as from a bent shaft. Both ball and tapered roller bearings have very limited internal misalignment capabilities. However, spherical roller barings have internal misalignment capability and can handle some degree of dynamic misalignment.

Basic Dynamic Rating:The Basic Dynamic Rating as defined by the American Bearing Manufacturers Association (ABMA) is the calculated, constant radial load which 90% of a group of apparently identical bearings with stationary outer ring can theoretically endure for a rating of 1 million revolutions (33 1/3 RPM for 500 hours). Basic Dynamic Rating is not the maximum load that should be applied to the bearing.

Static Radial Rating: The American Bearing Manufacturers Association (ABMA) defines Static Radial Load Rating as that load which corresponds to a total permanent deformation of rolling element and raceway.

Radial Load: Load acting on the bearing that is applied perpendicular to the bearing bore.

Axial Load: Load acting on the bearing that is applied parallel to the bearing bore. This is also known as thrust load.

Speed: Affects both the L10 life and operating temperature. Doubling the speed will reduce the L10 life by one-half and can cause a higher operating temperature. Speed is indicated in Revolutions per Minute (RPM).

Locking Mechanisms

Single Set Screw: Provides two setscrews on a single side of the bearing inner race to secure the bearing to the shaft.

Eccentric: Provides a collar with an eccentric lip that mates with an eccentric lip on the bearing inner ring. Turning the collar while holding the shaft and inner ring results in a “cam” action that locks the collar and inner ring to the shaft. (Eccentric lock is not recommended for reversing rotation applications.)

Concentric: Concentric locking mechanisms consist of either concentric collars or tapered adaptor sleeves. Concentric locking mechanisms center the shaft in the bearing bore and virtually eliminate the lock induced bearing out-of-roundness found with eccentric or setscrew designs. This reduces vibration and shaft run-out during operation, as well as eliminating shaft marring.


Pillow Block:The most widely used housed bearing unit. Available for light, normal, and medium duty applications.

Stamped Stell

Flange Bracket: Narrow housing with three bolt holes on one side of the housing. Best used in very tight spaces and tail pulleys.

flange bracket

Stamped Steel: Stamped steel housings typically consist of two steel halves that mate together and clamp the bearing insert. These are available in both pillow block and flange designs.

flange bracket

Two-Bolt Flange: Designed for flush mounting with machined bases for light loads and two bolt holes.

two bolt flange

Four-Bolt Flange: Designed for flush mounting with machined bases and four bolt holes.

Four Bolt Flange

Insert or VER Unit: Designed to mount in customer’s housing. These bearings offer no self aligning capability.

Invert or VER Runit

Tapped Base Pillow Block: Pillow Block units well suited for applications where shafts are close together.

Tapped Base Pillow Block