The Coupler Clamp "O" or cheeseborough style clamp. This clamp fits our 12'' I-beam, triangle and box truss and our 16'' box truss lines. The Coupler Clamp is designed to fit into the end of the truss and clamp to another section of truss. It works well for situations in which a corner can't be used. It clamps around 50mm (2'') OD tube.