What this topic chooses is the ball screw nut pair. Because the ball screw nut pair is a low friction, high precision, high efficiency of the mechanism, in the CNC machine tool widely. The transmission feature is that ball bearings are provided between screw nuts with screw grooves as intermediate transmission elements. When the screw and the nut move relative to each other, the ball rolls along the screw groove raceway, so there is basically rolling friction between the screw and the nut. Moreover, the friction coefficient of the ball screw nut pair has a very small difference. With the rolling guide, the starting torque is very small and the movement is sensitive. Ball screw nut mechanism is a rotating motion and linear motion mutually moving transmission assembly.