Rolling Bearings Terms and Definitions
Rolling bearings are essential components in machines and other equipment, which enable the efficient transfer of power and motion. As such, it is important to understand the essential terminology associated with rolling bearings and the functions of their components.
Angle Of Contact: The angle (alpha or β) between an inner race contact surface and an outer race contact surface when they are in mesh or contact.
Axial Pre-loading: The act of pre-loading a bearing with a predetermined axial force, usually radially mounted. The pre-load force acts to increase radial bearing stiffness and the bearing rigidity.
Back To Back Assembly: This term refers to two identical bearing assemblies that are closely opposed to one another and operated in perfect synchrony.
Bearing Clearance: The space between bearing components in the mounted bearing. This denotes the play between moving parts to allow for efficient function and movement.
Cage: A cage or retainer that can be fitted to bearings to space and separate the rolling elements of the bearing from one another.
Contact Angle: This is the angle between the bearing raceway and the rolling elements when they are in contact under a radial load.
Lubricant: A lubricant applied to the bearing for reducing friction, heat and wear. Lubricant is most commonly oil or grease.
Mounting Hex: The hex socket head and cap screws used for mounting bearings onto a shaft or a housing.
Mounting Rings: Collar-type rings that slide into grooves on the shaft or housing to provide axial retention.
Outer Race: The outer ring of a bearing, often referred to as the outer race.
Pitch Diameter: The diameter of the theoretical circle which runs halfway between the bearing raceway surfaces.
Radial Load: A load that acts upon the center point at a right angle to the bearing axis.
Roller Segment: The distance between any two adjacent roller contacts when in mesh with the bearing raceway.
Runout: The deviation of the circularity of the circumference of the radial bearing races from perfect roundness when spinning on its axis when used with gages or instruments.
Set Collar: A mounting device used to fix bearings to the shaft with an axial load. The set collar has grooves for receiving a ring of screws used for attaching to the bearing’s outer race.
Spanner Wrench: A tool used for quickly and easily mounting or dismounting bearings with an optimum pre-load.
Thrust Collar: A collar that fits over a thrust bearing’s outer races to secure the bearing to a stationary mount.
Tube Assembly: An axial bearing arrangement which consists of an inner and an outer race in which the rolling element is confined within a separated chamber.
V-type Seals: A v-ring (or lip seal) that helps keep out contaminants. It is most often used in automotive and industrial applications.
Vibration: The oscillation or shaking of a bearing or its components, caused by an external or internal force.
Waviness: The deviation from a straight line of the contour of a bearing or its parts.
Yoke Roller: A roller bearing with raceways which have a higher number of rolling elements in contact than with a standard roller bearing. This increases load capacity, reduces deflection and improves rigidity.
