Ordinary expansion bolts: according to the different bolt heads, they are divided into three types, namely (hexagonal head), (semi-round head) and (countersunk expansion bolts). The fixing of the expansion bolt is to use the slope of the expansion to promote the expansion to produce friction grip and wrapping force to achieve (fixing effect). The screw is threaded at one end and has a vertebrae at the other. Outer bread with an iron sheet, half of the iron cylinder has (a number of incisions), put them together into the hole in the wall, and then lock the nut, the nut pulls the screw outward, pulls the vertebral into the iron cylinder, the iron cylinder is opened, so it is tightly fixed on the wall and is generally used for (protective fence), air conditioning, etc. (cement), bricks and other materials fastening. However, it is not very reliable to fix, and if there is a large vibration (load), it may occur (loosening), so it is not recommended for the installation of ceiling fans, etc. The principle of the expansion bolt is to hit the (expansion bolt) into the hole on the ground or wall, tighten the (nut) on the expansion bolt with a wrench, the bolt goes out, but the outer metal sleeve does not move, so that the big head under the bolt will open the (metal sleeve) to make it full of the whole hole, at this time, the expansion bolt will (can not be withdrawn).