Coin holder ring. The top will hold a Canadian quarter coin (23.8mm, same as USA) with just a small clearance. It would, of course, need to be glued in. The ring size prints to14.3mm so would fit a N. American 3 to 3.5
If you would like a different size please get in touch here or at gslingeratrogersdotcom.
Of course, the coin does not come with it!
Take a look at the last photo which shows another variation of what I have done with this ring blank - this time with gold flake, paint and resin. (This is for sale privately if you want to contact me).