A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least three races to contain the balls and transmit the loads through the balls. In most applications, one race is stationary and the other is attached to the rotating assembly (e.g., a hub or shaft). As one of the bearing races rotates it causes the balls to rotate as well. Because the balls are rolling they have a much lower coefficient of friction than if two flat surfaces were sliding against each other.

Ball bearings, or deep-groove bearings, extend the working life of equipment by enabling wheels, pulleys, and other rotating parts to reduce friction and move smoothly. Ball bearings have a series of round balls encased in a housing and support high axial or low-to-moderate radial loads. Axial (thrust) bearings support loads parallel to the axis, such as those exerted by a table supporting a weight.