Adjustable gas blocks let you fine-tune how much propellant gas cycles your AR-15 action — critical for suppressor builds, short-barrel pistol uppers, and mixed-ammo setups. Available in .625″, .750″, and .875″ bore sizes to fit lightweight, standard, and heavy-profile barrels. Low-profile designs sit flush under free-float handguards. Dial in less gas for softer recoil, reduced BCG wear, and tighter shot-to-shot consistency.