The tolerance grade of the bearing is mainly determined according to the rotation accuracy requirements of the shaft to the support. Class 0: It is widely used in general bearing systems with rotation accuracy greater than 10um. Such as the variable speed mechanism of ordinary machine tools, feed mechanism, automobile, tractor variable speed mechanism, general motor, water pump and agricultural machinery and other general machinery rotation mechanism. 4, 2: In the rotation accuracy of less than 5um or very high speed of ultra-precision instruments, such as precision coordinate boring machine, precision grinding machine gear system, precision instruments, meters and high-speed camera precision systems. 6, 5 level: in the precision bearing system with rotation accuracy of 5-10 UM or high speed, such as the bearings used in ordinary lathes (front support with 5 level, rear support with 6 level) more precise instruments, meters and precision instruments, meters, and precision rotating mechanism