A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races.
A ball bearing for skateboard wheels with a plastic cage
Wingqvist developed a self-aligning ball bearing
In mechanical engineering, a rolling-element bearing, also known as a rolling bearing, is a bearing which carries a load by placing rolling elements between two concentric, grooved rings called races. The relative motion of the races causes the rolling elements to roll with very little rolling resistance and with little sliding.
Study of ball bearing by Leonardo da Vinci (1452–1519)
A gear bearing
A needle roller bearing
A prematurely failed rear bearing cone from a mountain bicycle, caused by a combination of pitting due to wet conditions, improper lubrication, improper pre-load adjustment, and fatigue from frequent shock loading.