The AR-F3 (Flattop FastFire Mount) is the simplest and most effective way to mount the FastFire II on an AR flattop stand alone or as a Co-witness for your iron sights. The FastFire sits inside the mount for extra protection, and it also features a compartment for carrying a spare battery, open end wrench and Torx wrench. Fits any Weaver or Picatinny style base.