MODEL RELEASED. Ball bearing manufacture. Worker visually inspecting a ball bearing as part of quality control during its manufacture. The bearings consist of two concentric rings with metal balls housed in a cage between them, so allowing one of the rings to rotate whilst the other remains stationary. The bearings must be machined accurately for them to work correctly. Ball bearings are widely used to reduce friction in mechanical machines. Once installed in a machine the outer ring is usually secured to a fixed structure whilst the inner ring is attached to a rotating shaft.