The 2A Armament(TM) Aethon Rail M-Lok series provides an alternative aesthetically progressive design that is lightweight with their signature titanium barrel nut and attach method. The innovative attachment of the rail and the barrel nut provides a solid lockup, a seamless, strong joint that requires no timed alignment to the barrel nut itself. All 2A Armament rails and receivers are designed with a pocketed picatinny rail to further minimize weight. With new styling and attention to detail the picatinny pockets taper at the end of both the upper receiver and the rail so that one can match the 2A rail to a third party upper if desired and still have a clean transition in the design. Note: a If you have an earlier Balios Lite receiver set you will want to use the first generation BL RAIL M-Lok series. a 1-5/16" crows foot tool or premium armorers wrench recommended for installation (Not Included)