Yesterday on the beach (old wharf/pier) I found an old time piece plate and a pocketknife. I also found a concave shaped item that originally had three attached eyelets so that the dome could be affixed to wood? It had brass readings on the metal detector (42-45) and is not perfectly domed. Maybe it covers a "grounding" wire bundle? My guess is it is circa 1930-1960. Anyone seen one of these?