TROY Industries A4 Complete Upper, 223 Rem/556NATO, 16 Barrel SUPG-A4S-16BT-00 Troy Industries AR-15 A4 Upper Receivers are lightweight and ultra-low profile. Developed specifically for today's war fighter and Law Enforcement led by Special Operations field requirements. The M-Lok SOCC handguard is lightweight with an ultra-low profile" snag-free design" they are ideal for close quarters maneuverability. Machined from hardened aircraft aluminum with stainless steel components and finished in Mil-Spec hardcoat anodizing. The M-LOK slots make for mounting your favorite M-LOK accessories quick and easy. The Troy Industries folding Battle Sights feature push-button operation and tool-less adjustment. Constructed of aircraft aluminum with stainless hardware. Battle Sights feature a zero cant mounting system ensuring perfect sight alignment. Sight mounts to the receiver with a cross bolt.