We then rolled the edge of inner panel. These mandrels provide a 1-inch radius once you mate up both pieces of sheetmetal. They are designed by Ron Covell to fit Pexto and other bead-rollers with 15/16-inch shafts. As with any bead-roller mandrels, make many passes and tighten the mandrels slightly each time. With the tank-roll dies, make sure to keep plenty of pressure against the inner lip of the dies so the sheetmetal doesn't slip out or "walk."