Vltor A5 Receiver Extension Black. This receiver extension is designed to work with Mil-Spec dimensioned M4/AR-15 type collapsible stocks. It also can be utilized as a replacement receiver extension for the AR-10 rifle. Six position receiver extension made from impact extruded 7075 T6 aluminum Hard coat anodized Positions are numbered and are visible through the witness hole on most stocks Snag-free sliding of the buttstock Receiver is designed to use the VLTOR A5 spring and buffer kit only which is sold separately. Receiver extension is Mil-Spec dimensioned and will only accept M4 type Mil-Spec buttstocks Weighs 4.2 oz Specifications for Vltor RE-10/A5SR-A5 Receiver Extension: Manufacturer: VLTOR Condition: New Package Contents: Vltor RE-10/A5SR-A5 Receiver Extension Vltor RE-10/A5SR: RE-10/A5SR-A5 Receiver Extension Black