The Wheeler EngineeringAA(R) 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 an AR 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.