I couldn’t live without this 25 piece set of long steel mandrels. They are sized in millimeters. The size ranges from 1 to 13 mm in ½ mm increments. The mandrels are nice and long for making long coiling or a larger batch of jump rings.
The second favorite in the picture is a round steel bracelet mandrel and it is ideal for shaping and forming . Being steel, I can hammer the metal on it.
The last is a steel ring, stepped mandrel, for forming, shaping, straightening, enlarging or gauging your wide-shanked rings. I also use this when I want to make larger jump rings. Here are a couple more sites to find great tools: