The SDTA adjustable gas block performs two main functions and advantages. We all know that AR15's are finicky when shot suppressed or with subsonic ammo. The SDTA gas block allows adjust ability of gas flow to easily tune your system to perfection. There is also a hidden quality...... Later this year we are in development of a over the barrel silencer system that will mate up with this gas block. All these features at half the price of the other gas blocks on the market. Made with 4140 steel.