LWRC's ICDI Upper Receiver is a perfect start to a custom AR build. It utilizes LWRC's direct impingement operating system with a keyless bolt carrier design and proprietary DI bolt carrier group. The 10.1-inch barrel features button cut rifling and features unique spiral fluting. The barrel is topped with 1/2x28" threads for muzzle devices and suppressors. Other features include an ambidextrous sling mount, an ambidextrous charging handle, an H2 buffer, and a carbine length action spring. Features of the ICDI Upper Receiver: LWRCI DIRECT IMPINGEMENT SYSTEM LWRCI COLD HAMMERED BARREL LWRCI PROPRIETARY DI BOLT CARRIER GROUPLWRCI AMBIDEXTROUS SLING MOUNT LWRCI AMBIDEXTROUS CHARGING HANDLE H2 BUFFER CARBINE LENGTH ACTION SPRING LWRC International LWRC ICDI M-LOK Direct Impingement 5.56mm NATO 10.5" 1:7" 1/2x28 Bbl FDE Complete Upper Receiver ICDIU5CK10ML