The space occupied by the hollow shaft is relatively large, but the weight can be reduced. According to the mechanical analysis of the material, when the torque is transmitted through the shaft, the effect of transmitting the torque is greater as the outer section is viewed from the radial section. A thicker shaft diameter is required when the shaft needs to transmit a large torque. Since the effect of transmitting torque at the axial portion is small, hollow is generally used to reduce the weight of the rotating shaft.