This sight set is made from 6061 aluminum and Mil-Spec 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 flip-up front sight is HK configuration. The A2 flip-up 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.