What sets the M4 RAS besides other 2-piece quad rails available is that it securely locks into the rifle’s barrel nut by using a clamp and screw arrangement, which makes it a really solid foundation on which to mount tactical accessories. Consists of a few KAC eleven Rib Rail Panels. https://knights-armament-rail40739.goabroadblog.com/26415720/what-does-kac-ras-rail-mean