The fixing principle of the expansion screw: the fixing of the expansion screw is to use the inclination of the shape to promote the expansion to produce the frictional binding force to achieve the fixing effect. One end of the screw is threaded, and the other end is tapered. There is a steel skin on the outside. Half of the iron skin cylinder has several cuts. Put them together into the holes made in the wall. Then lock the nut. The nut pulls the screw outwards and pulls the cone into the steel skin cylinder. The steel skin is round. The tube is expanded, so it is tightly fixed to the wall, and is generally used to fasten protective fences, awnings, air conditioners, etc. on cement, bricks and other materials.