Universal Dual Sides Picatinny Rail Rifle Barrel Mount Tube Adapter Solid Aluminum Construction with Matte Black Finish Smart 2 Piece Design for Clamping Rifle Barrel Compatible Barrel Range: Diameter 12-20mm Installs Easily and Wrench is Included, we provide two sets screw for you(long screw and short screw.if you not received two sets screw, pls contact me ) Great for install barrel mount flashlight, shotgun,Laser Sight, Bipod,etc.