Image Number 4 for United States Patent #6447227.
A threaded fastener which includes a shank, a radially enlarged head at one end, an external thread on at least a part of the shank, and a bore which extends through the head and into the threaded part of the shank. At least the threaded part of the shank is radially expandable into the threaded engagement with the wall of a suitable unthreaded bore in a workpiece in which the threaded part has been inserted. The fastener thereafter is removable by unscrewing it from the workpiece bore. The expandable part of the shank is provided with a plurality of radially extending lugs or other protrusions provided on the threaded part of the shank thereby to resist unscrewing of the fastener from the workpiece bore.