Knight's Armament URX (SR-25 Rifle). Identical to M-110 SASS rail except it's black in color. Rail is approximately 12 1/2" long. Free floats the barrel, bottom rail is removable. Has a built in flip up front sight. Picatinny rails on all four sides allow endless possible mounting solutions for accessories such as sling mounts, vertical forearm grips, bipods, flashlights and more. Will only fit SR-25 or DPMS "High" patterned uppers such as Mega, DPMS, Aero Precision, will not fit the Armalite AR-10 receiver threads. Installation available, special tools required.