The Wheeler Universal Barrel Clamp is precision extruded from aircraft grade aluminum and bonded with non-marring urethane. The urethane coating is specially designed to provide a protective layer for the barrel's finish while providing extraordinary gripping abilities. Three different barrel openings of.85",.66" and.53" will accommodate anything from a tactical rifle pencil barrel up to a bull barrel. When inserted in a vise the urethane coating squeezes down tightly on the barrel to fully secure it for the forces needed for installation/ removal.