The Adams Arms Standard Pistol Length Piston Kit is a short stroke free-floating piston system that is self-cleaning and has a corrosive resistant coating. The kit includes: one-piece bolt carrier, .750" Picatinny gas block with 3 settings, gas plug, bolt spring, drive rod with bushing and spring. This model requires a pistol gas length 4.846" from barrel extension to shoulder and a .750" gas seat.