Hollow shafts take up more space but reduce weight. According to the material mechanics analysis, when the torque is transmitted by the rotating shaft, the effect of effective torque transmitted from the outside is greater from the radial section. A thicker shaft diameter is needed when the shaft shaft needs to transmit a larger torque. Due to the transfer of torque in the axis part of the role of small, so the general use of hollow, in order to reduce the weight of the shaft.