Samson Folding Front Sight HKFlip Up Rear Sight Set Blackbr All sights are made from 6061 aluminum mil-spec hardcoat anodized for durability br All of the sights lock in both deployed and folded positions br The spring mechanism is quite durable and is completely concealed to prevent fouling from dirt br The dual aperture rear BUIS has a conventional large and small aperture br The rear sight deploys with the large aperture