The Knights Armament Airsoft URX 3.1 Rail System 13.5" is an excellent upgrade or replacement rail system for any airsoft rifle. Built entirely from high strength, lightweight aluminum, this RIS system bridges the gap between picatinny rail utility and smooth handguard comfort. Add-on rail segments can be attached along the sides of this rail is additional accessories need to be mounted. The URX RIS has two integrated QD-sling mount attachment points for additional utility. If you're looking for a unique rail system, the URX is an excellent choice for any M4 platform that will give you a functional and unique look unmatched in airsoft.