The Knight's Armament Corp. Upper Receiver Extending 4 (URX4) is KAC's entry into the low profile, keymod rail market.



This rail is extremely unique in that is is monolithic in construction: the rail body is also the barrel nut! Included with the rail is a proprietary wrench for the URX4 system, as well as shims for timing the rail when tightening it on a upper receiver at 60-70 foot pounds.

*Includes shim set and wrench.