The installation surface of the shaft and the ring gear is required to have the same flatness, perpendicularity, roundness and cylindricity as the fine bearing. Controlling these form and position common services can not only achieve better installation accuracy, but also prevent excessive eccentricity of the inner and outer rings of the bearing from causing stress concentration and prolong the service life of the bearing. Regarding the processing specification of the shape and position common service, it is recommended to consult the bearing supplier to match the bearing accuracy.