Bearing (" Bearing ", the Japanese say "axis") is fixed in the process of mechanical transmission parts and reduce the load coefficient of friction. In other words, while other parts to each other on the shaft relative motion, is used to reduce the coefficient of friction in the process of power transfer and keep the shaft center position fixed part. Bearing is a kind of important modern machinery and equipment parts. Its main function is to support the mechanical body of revolution, to reduce the equipment in the mechanical load coefficient of friction in the process of transmission. By the frictional properties of motion elements, bearing can be divided into two categories, the rolling bearing and sliding bearing.