Bearing

A bearing is a component that lets one part rotate or move against another with minimal friction, while carrying load.

Rolling elements (balls or rollers) or a smooth sliding surface separate the moving parts, reducing wear and the power lost to friction, and locate the shaft against radial or axial loads.

Bearings appear in wheel hubs, the gearbox and drivetrain, the engine, and many pulleys and shafts. The correct bearing depends on the load, speed, and the housing it fits.