According to the ISO classification standard, precision bearings are divided into: P0, P6, P5, P4, P2. The grade increases in turn, among which P0 is ordinary precision, and other grades are precision grade. Of course, different classification standards and different types of bearings have different classification methods, but the significance is the same. The performance of precision bearing requires that the rotating body should have high beating precision, high-speed rotation and small change of friction.