The PMA Low Profile Steel gas block is the finest in quality and style for your AR-15 pattern rifle. They are precision machined from 4340 steel and Salt Bath Nitrided (Melonite). This treatment provides a harder-than-chrome surface with excellent lubricity and extreme corrosion reisistance. Matched with a slim, sculpted design, this gas block is perfect for mounting beneath a free-float rail system. These come with 2 mounting screws and the Carbine length gas tube installed with a stainless steel roll pin.