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 ICDI M-LOK Direct Impingement 5.56mm NATO 10.5" 1:7" 1/2x28 Bbl Black Complete Upper Receiver ICDIU5B10ML