Bearing is a kind of mechanical element that limits the relative motion to the required range of motion and reduces the friction between moving parts. The design of bearings can provide free linear motion of moving parts or free rotation around a fixed axis, and can also prevent movement by controlling the vector of normal force acting on the moving parts. Most bearings promote the required movement by minimizing friction. Bearings can be widely classified according to different methods, such as the type of operation, the allowable movement or the direction of the load (force) applied to the part.