The expansion screw is composed of a screw and an expansion tube. The screw tail is conical. The inner diameter of the cone is larger than the inner diameter of the expansion tube. When the nut is tightened, the screw moves outwards, and the conical part moves by the axial movement of the thread, and then the expansion tube. The outer surface bolt type composite cable bracket forms a large positive pressure, and the angle of the cone is very small, so that frictional self-locking is formed between the wall, the expansion pipe and the cone, thereby achieving a fixed effect. For example, the Sanfeng composite cable bracket is self-locking through friction between the wall, the expansion tube and the cone to achieve a fixed function.
