In the gas cylinder screw photos above, the slot appears to have been made by three drilling operations, one on each side and a larger one in the center. I have what I suspect is a reproduction. The slot appears to have been cast. The opening is smooth and regular in shape, but the inside walls are rough. Can anyone confirm that it is a reproduction. Also, in checking two post war screws, they both are attracted to a magnet as is the reproduction. What material were the early screws made of.