M4x20mm Socket Head Expansion Bolt Sleeve Anchor 30pcs

Expansion anchor bolt. Features a round slotted/ head. The working principle of expansion screw:?Put the expansion screw into hollow 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. Can installed on the plasterboard cavity wall to hold shelf curtain rod hallstand lamps.