The three letters URX may refer to: British Rail used the acronym "URX" to refer to an Under Road Crossing, and it still appears as such on maps Knight's Armament Company's Universal Rail eXtension - an adapter system for adding components to firearms "URX" is the stock ticker symbol for United Refining Energy Corp., listed on NYSE MKT (formerly AMEX - American Stock Exchange) The Picatinny rail, an adapter system similar to KAC's Universal Rail eXtension, is also (incorrectly) referred to as "URX"