According to the different loads of the shaft, the transmission shaft can be divided into: the rotating shaft, the spindle and the transmission shaft.
Rotating shaft: it not only supports transmission parts but also transmits power, that is, it bears bending moment and torque.
Mandrel: it only supports rotating parts without transmitting power, that is, it only bears bending moment.
Transmission shaft: it mainly transmits power, that is, it mainly bears the action of torque.
For example, "the front and rear axles of a bicycle are only supporting parts and do not transmit torque. They are mandrels". The middle axle is a rotating shaft, which is subjected to both bending moment and torque. The front and rear axles of a bicycle are mandrels and only bending moment. But which is the transmission shaft? It is the middle axle. Only it rotates among the three shafts. The front and rear axles only play a supporting role.