The Adams Arms Standard Carbine Length Piston Kit is a short stroke free floating piston system that is self-cleaning and has a corrosive resistant coating. The kit includes a one-piece bolt carrier, .750" Picatinny gas block with 3 settings, gas plug, upper receiver bushing and installation rod, bolt spring, drive rod with bushing and spring,. This model also includes an installation DVD and requires a carbine gas length 7.866" from barrel extension to shoulder and a .750" gas seat.