This thing is about 3 1/4" in diameter, and seems to be made of pot metal/pewter/cast aluminum. On one side, It has numbers 1-12 like a clock, and 1956 in the middle. The other side also has numbers 1-12, with a dash, and then 56 too, but, these numbers are backwards/reversed like for a printing plate. What do you suppose this was used for? Printing just the month and year (I presume 1956) seems a bit odd. Did it fit some sort of machine? I don't see any attachment point on it, and the shape seems strange for a printing plate.