The PM138 front sight body and stem are machined from T6 aircraft grade aluminum and type III hard anodized. Steel parts are machined, then black phosphated per mil-spec. Precision machined to fit dovetailed gas blocks meeting MIL-STD 1913 Picatinny rail specifications. The sight is mounted to the gas block via a locking bar and secured with a cross slotted, knurled thumb screw. The sight is adjustable for elevation, (a quarter turn) moving the point of impact 1.25MOA (minute of angle) at 100 yards. The front sight features straight protective ears. The sight's stem folds up and towards the shooter to deploy. When in the up position the sight is locked in place via a spring loaded plunger. To fold the sight to the down position, depress the plunger and fold the sight stem forward. No permanent modification required for installation. All hardware included. The PM138 sight may be paired with model PM136, PM137, PM200 PM202 rear sights mounted to AR-15 / M16 flat top A3 upper receiver rifles and carbines.