So I've recently watched Tommy Wonder's Vision of Wonder and there was a gimmick in there which I can't tell where to get or what it was. It had a washer on one side, coin on the other. A hole goes all the way through, and a shell covers the washer and has a piece on it that fills the hole. It's difficult to explain. you could watch the "socked coins" part of visions of wonder if you want to see what it looks like.