The hook shall be free of defects that may affect the safe use performance; The hook defects shall not be repaired by welding; The surface of the hook shall be smooth and free of cracks, folds, acute angles, burrs, peeling, burning and other defects. Two suitable positions can be selected at the shortest distance of the hook opening to print signs that are not easy to wear, and the distance of the signs can be measured as the basis for detecting whether the opening degree changes during use.