Self Drilling Concrete Snap-Off Anchors are a two-piece assembly for us in masonry. The body of the fastener is threaded one end and the other end is slotted to allow for expansion, and sharp teeth to drill into the masonry. When the hole has been drilled, a conical plug is placed in the bottom of the hole, and the fastener body is hammered onto the plug, expanding it and locking it in place.