Ring Sizers, Finger Sizers, and Tools for making your own rings:
Metal ring mandrels are a standard jeweler's tool: you can use a nylon hammer or rawhide mallet to reshape or enlarge (re-size) rings, as well as texture or stamp pewter, aluminum and sterling silver rings. However, they are heavy to ship.
Plastic ring mandrels are great for use with metal clays! Plus they are lightweight (easy to ship and grip), but don't withstand as much abuse (such as hammering).
Ring-bending pliers make it a breeze to shape up to 14-gauge metal into a nice round ring.
Ring clamps hold a ring while you polish or grind, and are also excellent for holding layers of flat metal while you drill or rivet.