The Phase 5(TM) Universal Mini Stock (UMS) is a fixed stock solution for your rifle that fits on a variety of buffer tubes and receiver extensions. The UMS offers a smaller footprint and bottom curve which makes for a far superior anchor of the stock on the chest. This allows an operator to get in and out of postion with greater of ease. Utilizing two heavy duty set screws, the UMS offers easy installation on receiver extension tubes.*The Universal Mini Stock (UMS) is a stock to be installed on a rifle. Installing a stock on a Pistol would be considered an SBR (short-barreled rifle). If you don't have the required tax stamp, it is illegal to possess an SBR.Compatibility: Mil-Spec 6-position carbine receiver extensions Phase 5(TM) HexOne Buffer Tube Phase 5(TM) Hex-2 Buffer Tube Most cylindrical buffer tubes, 1.10"-1.25" OD* Rifle length receiver extension tube**The set screw will be more secure on the cylindrical buffer tubes if you put a small dimple on the tube.There will be empty space between the stock and tube with most cylindrical tubes.