At the end of main screw, a screw hole with inverse thread is drilled and a small screw is screwed in and has antislip veins on the inner side of its died nut.

• 本发明技术构造在主螺杆外端头打一反丝螺孔，配以小螺杆，小螺杆死帽内侧有防滑纹，主螺帽外侧有防滑纹。