The Nordic Components standard shotgun barrel clamp provides extra rigidity for your magazine extension. Each clamp half has a centrally-located 10-32 threaded hole to accept accessories, such as a sling stud, barrel clamp tac rail or QD sling mount. Designed for Nordic extension tubes (1.060" diameter).Features :Threaded Hole to Accept AccessoriesProvides Extra RigidityDesigned for Nordic Extension Tubes (1.060 Diameter)