The position accuracy requirements of shaft parts are mainly determined by the position and function of the shaft in the machinery. Generally, it is required to ensure the coaxiality of the shaft journal of the assembled transmission part to the supporting shaft journal, otherwise the transmission accuracy of the transmission part (gear, etc.) will be affected and noise will be generated. For ordinary precision shaft, the radial runout of the matching shaft section to the supporting journal is generally 0.01 ~ 0.03mm, and for high-precision shaft (such as main shaft), it is usually 0.001 ~ 0.005mm.