Knight's Armament URX 1 (SR-25 Carbine). Rail is approximately 10" long. Free floats the barrel, bottom rail is removable. Picatinny rails on all four sides allow endless possible mounting solutions for accessories such as sling mounts, vertical forearm grips, flashlights and more. The URX comes with three 11 rib panels to help protect the rails from damage. Includes built in flip up front sight. Will only fit SR-25, will not fit the AR-10. Installation available, special tools required.