The RFB Quad Rail is made from hard coat anodized 6061-T6 aluminum and is approximately three inches long and will accept any accessories which mount with a standard MIL-STD 1913 Picatinny Rail attachment. The two scalloped cut-outs on the top of the Picatinny allow the shooter freedom to adjust the gas system if needed and allow the ejected casings to leave the ejection port. The shooter should take caution on which accessories to mount on the left hand side of the weapon since this could block the ejection port. Includes : (1) RFB-420 Quad Rail (1) Locking Nut & Wrench (1) Set screw with Hex Key