1.Applications: be widely used in fence, burglarproof doors and windows, canopy, air conditioning rack fixation, home decoration, engineering, etc.
2.The working principle of expansion screw:  Put the expansion screw into the ground or the hole on the wall and then tighten the nuts of the expansion bolt with wrench. The bolt goes outside while the metal sheath does not move. Thus the bigger head of the bolt will expand the metal sheath, making it fill the whole hole. Now, the expansion screw can not be pulled out.