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