Anchors are generally said to be metal expansion screws, they are fixed using a wedge-shaped slope to prompt the expansion of frictional grip force to achieve a fixed effect.
One end of the bolt is threaded, one end has a taper. The outer wrapping a tin (some are steel), tin cylinder (steel) half of a number of cuts, stuff them together into the hole in the wall and then lock the nut, the nut pulls the screw outward, and the taper will be pulled into the tin cylinder, the tin cylinder is raised, so tightly fixed on the wall, generally used for protective fences, canopies, air conditioners, etc. in cement, brick and other materials fastened