The copper wire rod and the copper nut are a pair of friction pairs. The reasons for choosing copper materials for the friction pairs are as follows:

　　One is to greatly reduce the friction coefficient, so the first is to greatly reduce the friction, and the operation is labor-saving and convenient; the second is to reduce the loss (wear) and increase the service life;

　　Second, it is not easy to seize, so the gap between the screw rod and the nut can be made small, which can improve the accuracy of the equipment;

　　In addition, the choice of copper which is not only hard to wear but also softer than the screw, can protect the valuable parts of the screw from wear and make it more durable.