Wheel rim is used for holding the tube and wrap up the envelope. 1. During the curing, it can hold the tube and wrap up the envelope at the side of tire. 2. If choose double envelope, no need the wheel rim 3. It made by 16Mn spring steel punch, and forming with one time, it isn't out of shape. 4. Size: 10", 12 ", 13 ", 14 ", 15 ", 16 ", 17.5 ", 18 ", 19.5", 20 ", 21", 22.5 ", 24", 25 ", welcome special size order.