This sight set is made from 6061 aluminum and MilSpec hardcoat anodized for durability. Sights lock in both deployed and folded positions. The spring mechanism is quite durable and completely concealed to prevent fouling from dirt. The flipup front sight is HK configuration. The A2 flipup rear sight has a dual aperture with a conventional large and small aperture. The sight deploys with the large aperture. It is not intended for lower height gas block rails. M4 Cowitness height.