The addition of a suppressor, dirty conditions or even switching ammo are all factors that can lead to undesirable gas settings on your rifle. Our patent pending design was initially developed to fulfill an order in our Government programs which required the ability to run suppressed or unsuppressed in the field. The Select Adjustable Gas Block allows a near infinite initial adjustment using an allen wrench. To begin, simply turn the gas screw in (reducing gas) or out (increasing gas), whichever you require, and finish by attaching the gas switch for tool-less, on the fly adjustments without losing your initial gas setting. Features: 40-position fine adjustment Tool-less gas selection switch Suppressed or unsuppressed