Description We highly recommend using the newer combined 5.56/300BLK ZRC version instead of this product since it uses an internal U-bracket with two clamps, providing an even tighter lockup of the handguard to upper receiver. It also works with both SIG and MI SD and standard handguards. You can find it here. Installation Guide 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. This version is designed for the MCX Virtus chambered in 5.56mm with either the Sig Sauer OEM slim handguard or Midwest Industries standard M-Lok handguard. A different version for use wi Mfg: Arisaka Defense