A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can handle. So by definition the bearing industry is a specialized branch of machine building that produces antifriction bearings, plain bearings, and parts for antifriction bearings. All forms of production are combined in the bearing industry: mass, large-series, and lot. Much of the production is automated.