It's about the size of a silver dollar.
Nothing from this site is new. The civil war is the newest that I've found here so far. That's one reason why my curiosity is up.
See that square axle on one end. I expect that little drum has a clock spring inside of it. When I first saw this thing I thought "Bleeder/leach" and I don't know why because I've never seen one made like this. They were still used in the civil war which really mystifies me. Most fatalities were caused either by exsanguination or pneumonia.