NcSTAR Keymod Rail System/Carbine Extended Black 13 in Length VMARKMCE. Specifications for NcStar Keymod Rail System: Designed to fit AR15/M4s with: MIL-SPEC Barrel Nut Delta Ring and front Handguard Cap. Length: 6.5" Weight: 5.9 oz. / 7.9 oz. with...