An adjustable gas block lets you tune how much gas cycles the rifle, and that pays off two ways: less recoil, and cleaner running when you shoot suppressed. This one has a .750 inner diameter, the most common size, and a low profile that fits under free-float handguards. A front screw adjusts gas flow, and a side set screw locks your setting so it doesn't drift. Manganese phosphate finish. Hardware is included: two set screws, a roll pin, and both adjustment screws.