These low profile gas blocks are the ideal companion for lightweight AR-15 barrels with a .625 diameter gas shoulder. Made from high-strength steel, these gas blocks are industry standard.This Low Pro Micro gas block replaces the existing A2 front sight, and is sleek and small to allow a longer rail to be placed over. It is constructed of CNC steel and compatible with 5.56/223 firearms with a .625\" diameter barrel. A roll pin & set screws are included.