Lets You Tailor Extraction & Ejection To Individual Loads Lightweight, steel gas block features an adjustable gas port that lets you tune the amount of gas for reliable extraction and ejection to match your ammo. Adjustment screw closes or opens the port in the block and not the gas tube; drilling of the gas tube is not required. Fits under free float tubes and does not interfere with sight picture through scopes or red-dot sights. Dual set screws on bottom of the block securely locks the block onto the barrel.