12 gauge roll crimping tool. Used for gently rolling the plastic hull inward over the contents for professional looking results. Absolutely mandatory when loading magnum shot shells, tracers, slug loads, etc.. A roll crimp takes up less of the hull than the standard star crimp and promotes longer case life and better seals. Comes with instructions. Fits in standard drill press, friction heats the hull and rolls it inward to the overshot card. Takes only seconds.