Arisaka Defense MCX Zero Retention Clamp, Fits Sig Sauer MCX, 7.62 Standard Handguard, Anodized Finish, Black ZRC-SPEAR-H The Patent Pending Arisaka Zero Retention Clamp (ZRC) greatly reduces zero shift for lasers and iron sights that are mounted on the handguard of the MCX Virtus and Spear LT. This version is designed for the MCX Virtus chambered in 5.56 and 300BLK" and the Spear LT chambered in 5.56" 7.62x39" and 300BLK. The Rattler is not currently supported. The MCX Virtus and Spear LT handguards are not adequately secured to the upper receiver. This allows the handguard to flex significantly" causing a laser or front sight zero to change when minor pressure is applied to the handguard. A shift of 5 mils or more is possible by pushing on the handguard with your support hand while the rifle is shouldered. Additionally" the zero does not always return to it's original position once pressure is removed from the handguard. The Arisaka ZRC consists of exterior clamps that thread into a special U-bracket. The U-bracket engages the extended upper receiver underneath the handguard. This secures the handguard tightly to the upper receiver across two axis" greatly reducing or even eliminating zero shift. The U-bracket does not touch the barrel or gas system" preserving the free-floated barrel. The ZRC clamps are contoured to provide minimal interference with the user's hands while gripping the handguard.