Abstract: An anchor for insertion into a hole in a wall having an undercut groove extending therearound, the anchor having an elongated body with a bore therethrough, the bore being threaded at its outer end and tapering down in diameter toward the inner end of the body and slotted to permit expansion when a tapered pin is inserted therein. The body has an annular locking collar about its expandable portion placed to enter the groove when expanded. The groove and locking collar precisely interfit and are spaced from the inner end of the hole and the anchor body by a distance at least as great as the axial width of the collar. A screw member fits in the bore and has a pusher pin which pushes the expansion pin all the way into the bore when the member is screwed partway into the threaded bore portion, leaving part of the screw protruding from the body and the hole.