The key to determining bearing tolerance grades is based on the requirements for the rotational accuracy of the shaft relative to the support.

Grade 0: Generally used for bearing systems with rotational accuracy exceeding 10 microns. This is widely used. Examples include the speed control mechanisms and tool feed mechanisms on ordinary CNC lathes, the speed control mechanisms of automobiles and large tractors, and the rotating mechanisms of common chemical machinery such as motors, centrifugal pumps, and agricultural machinery.

Grades 6 and 5: Used in precision bearing systems with rotational accuracy of 5-10 microns or higher speeds, such as bearings commonly used in CNC lathes (Grade 5 for the front support, Grade 6 for the rear support), as well as in more delicate instruments and equipment, instrument panels and their instruments, and precision rotating mechanisms.

Grades 4 and 2: Used in ultra-high-precision instrumentation, such as the transmission gear systems of precision milling and grinding machines, as well as in instruments, dashboards, and high-speed cameras, with rotational accuracy of no more than 5 microns and relatively high speeds. This is the old designation for precision grades of bearings in China.

International specifications are all formulated in accordance with ISO standards and are generally aligned with them, sometimes even more stringent. The accuracy is divided into specification accuracy and rotation accuracy, which are 0 degrees, 6X degrees, 6 degrees, 5 degrees, 4 degrees, and 2 degrees.