Back bolt refers to the small anchor bolt used on the back of curtain wall plate to connect curtain wall plate and pendant. It is a bottom-expanding mechanical anchor bolt, which is usually divided into back bolt screw, expansion piece, sleeve and nut. It is made of stainless steel (304,316), and M6 and M8 back bolts are the most widely used in engineering. Technically, the imported anti-loosening back bolt should be more advanced. There are also common rotary back bolts and impact back bolts. Because the rotary back bolt is split, there may be safety hazards. In some places, this kind of back bolt has been gradually abandoned, so the most commonly used in engineering is the impact back bolt. Because it is directly knocked, it may lead to cracks and dark lines on the board, and the cost and risk will rise (mainly because there is no good means to detect dark lines at present). At present, the best imported brands in China are Yu Hui, Hilti and Baylord. Steyr, swordfish, Dali and other domestic brands can be compared! Handmade, hope to adopt!