Knight's M4 R.A.S. replaces the standard hand guards on 14.5 & 16 inch MILSPEC carbine barrels. Installation takes about 5-10 minutes and only requires an allen wrench. Picatinny rails on all four sides allow endless possible mounting solutions for accessories such as sling mounts, vertical forearm grips, flashlights and more. The M4 R.A.S. comes with three 11 rib panels to help protect the rails from damage. This version includes the upgraded UK/SAS lower rail which also clamps to the barrel nut which makes it rock solid.