Burris' AR-F3 is the simplest, most effective way to mount any FastFire sight on an AR flattop. It also allows the FastFire to mount be at the optimum height, so the red dot can co-witness with flip-up sights. The metal wings protect the lens, and the lower compartment stores spare battery, open-end wrench, and a Torx wrench. This model is compatible with Weaver or Picatinny-style base. Features: Simplest, most effective way to mount any FastFire sight on an AR flattop Allows the FastFire to mount at the optimum height, so the red dot can co-witness with flip-up sights Fits Weaver or Picatinny style base Metal wings protect the lens from impact and unintentional abuse Lower compartment stores spare battery, open-end wrench, and Torx wrench