My dad was on submarines in the 1960s, and he said they would file down large lug nuts with a diamond file to make rings like this. Not sure if this is the same, but it would be a good way to pass the time. He still wears his every day!
Another question, has anyone tried to clean one of these? It's stained up, but I'm sure they'll come out, and it smells god-awful to be honest... I'd like to stick it in the washer, think it'll survive?