Bruce has been contacted, he has these available in different materials. I didn't personally talk with Bruce, but I was told he primarily machines these plugs out of aluminum with a slight taper(how much, I don't have a clue), then you drive the plug in and finish flush with grinder if necessary, then cold galv the repair plug.
Another thing we do is punch the holes rather than drill, so our holes are not a true dimension on both sides of the material(ie. the entrance and exit dimn of the punched slug differ)