A metal fastening or joining apparatus is provided. In another aspect, a single piece die guard includes an integral die shield section and an integral retainer section, wherein a die anvil can be removed, and the die shield section has a low height and a small lateral square width. A further aspect employs a generally square peripheral shape for a die shield within which is an anvil and movable die blades, which are operable to fasten or join sheet metal workpieces together in an interlocking manner. In still another aspect, a projecting and/or peripheral orientation structure is on a backside of a workpiece fastening die assembly which allows for anvil reorientation without the need to also reorient a laterally surrounding die shield and retainer.