Knight's M4 RAS (Rail Adapter System) was developed for use on the US military's M4 Carbine, and with over 1 million rails issued to date, it is one of the most battle proven designs available for the AR-15 platform. This non-free float handguard is a simple-to-install, drop-in upgrade that features genuine Mil-Spec M1913 Picatinny Rails along its entire length. What sets the M4 RAS apart from other 2-piece quad rails on the market is that it securely locks to the rifles barrel nut via a clamp and screw arrangement, making it a very solid foundation upon which to mount tactical accessories. Includes three KAC 11 Rib Rail Panels.Rifle Requirements- The M4 RAS is a drop-in replacement part for standard, 2-piece polymer, M4-type handguards. The rifle must have a carbine length gas system, delta ring assembly, fixed front sight/gas block and round handguard end cap. Lighter barrel profiles work best (M4 or Government contours). Heavier barrel contours may require modification to the inside of the rail. *For AR-15/SR-15 based platforms only; not compatible with SR-25 variants. Installation instructions are included.