I made this tool a while back, actually, but I forgot to upload it. It was nearly completed before one of my low days hit me and it was shelved for quite some time before I finished it.

I need no explain to the view how I made it exactly, because it is already shown in the image.
The use of the tool is to be a punch and a compass that scribes a scratch line into metal in the shape of a circle. Simple enough.
I learned this from a smith on YouTube. I'm actually rather embarrassed that I don't remember, but I think it may have been an old timer like Mark Aspery