Cool find It is eather a shoe or a die out of a stamp mill . The shoe went in the bottom of the battery box and the die went in the boss head on the stamp stem as time went on they would wear out thus needing to be replaced.You can find a lot of them at my place in the old tailing piles. Some have gold on them also but I have never seen one with that much on it. I have a old stampmill that I need to get running someday. Might be fun