US Patent 7144212 Self-drilling hollow wall anchor

A high strength failure-resistant hollow wall anchor having a self drilling threaded installation structure adapted to be broken, after positioning, by an inserted screw, into expandable anchoring elements. The anchoring elements engage internally formed cams and the distal surface of the wall into which the anchor is deployed and are comprised of a plastic sufficiently rigid to effect a threaded insertion and to be broken apart, but which plastic is also sufficiently flexible to be able to form the expansion anchor member on the distal surface of a wall. The anchor includes anti-rotation elements to retard overtightening and anchor removal prior to screw removal.