Pantheon Arms Barrel Stop Dolos Equipped AR-15 Universal Black Oxide. Note: The barrel stop is not compatible with two-piece pinned aluminum lock collars (2016 production). Lock collars produced prior to October 2017 will need modified by drilling three holes (template coming soon) to allow access for an Allen wrench. Your barrel profile must have at least 0.800 of flat surface with a diameter of 0.940-1.000 to install the barrel stop. Specifications for Pantheon Arms Barrel Stop for Dolos Equipped AR-15: Manufacturer: Pantheon Arms Gun Model: AR-15 Color: Black Finish: Oxide Additional Features: Universal Condition: New Package Contents: Pantheon Arms Barrel Stop for Dolos Equipped AR-15 Pantheon Arms BSU: Barrel Stop Dolos Equipped AR-15 Universal Black Oxide