Fastener of high prevailing torque, pulling force, and stripping torque

This invention relates to a fastener, which expands by the insertion of an expanding member, preferably a screw. The fastener comprises a substantially flat head and two expandable legs. The head has an upper side and a lower side, preferably separated by a gap. The head has also a hole on the upper side in which the screw engages. Further, the screw engages in other locations of a critical portion of the rest of the body of the fastener, thereby increasing considerably the prevailing torque required to render the screw loose, the pulling force required to break the fastener or otherwise pull the screw out of the engageable hole of the upper side of the head, as well as the stripping torque.