Nordic Components Shotgun Barrel Clamp, Designed for 12GA MXT Extensions, Compatible with Most 12GA Shotguns, Features 10-32 Threaded Hole On Each Side for Mounting Accessories and Rails, Not Compatible with Mossbergs, Benelli Nova/Super Nova BCL-12 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).