It was probably much smaller. it may have been a straight pin that split the plating. After the zinc gets oxygen, then the coin starts to break down. If it were a hand punch or nail it would have created a raised area on the opposite side of the coin. Remember be are looking at things with a microscope. When looking at coins under a scope, try touching the coin with a toothpick. It looks like a pencil. So we need to keep this in mind when looking at coins with magnification.