A used Centurion C4 9 inch carbine rail in black. Mounts to a standard AR barrel nut, no fancy proprietary nonsense. Includes all mounting screws and bolts, and can include a compatible CMMG barrel nut for extra. I ship via UPS, shipping not included in price. State quarantine may affect ability to send and receive. I'm always down to trade for real steel or GBBR gear.