Vltor Re1 AR-15 Receiver Extension AR-15 Aluminum Black The Re-1 Receiver Extension Allows You To Mount a Mil-Spec Stock On a Civilian Carbine Or Convert Your A2 Style Fixed Buttstock To a Collapsible Configuration. This Receiver Extension Has Five Positions And Corresponding White Position Numbers That Are Visible Through The Witness Hole On Most Stocks. It Is Made From Impact extruded 7075-T6 Aluminum With Hard Coat anodized Finish. It helps With Snag-Free Sliding Of The Buttstock. Type: Extension Tube Model: AR-15 Finish: Black Material: Aluminum