Spline shaft is a kind of mechanical transmission. Like the action of flat key, semi-circle key and oblique key, spline shaft transmits mechanical torque. There are longitudinal keyways on the surface of the shaft and corresponding keyways on the rotating parts of the shaft, which can keep synchronous rotation with the axis. At the same time of rotation, some can also make longitudinal sliding on the axle, such as gearbox gear shifting, etc.