The Cobalt Kinetics CK-Pro receiver sets were designed for end users that want to build the very best AR by using the best receiver set you can source for your project build. The design for our upper receiver features our proprietary receiver extension that gives your barrel a rock solid foundation and secures the handguard onto the upper receiver via 8 TORX head screws giving you a TRUE non-rotating system. You will be able to enjoy the features of a mono-lithic upper receiver without the same drawbacks that a mono-lithic upper receiver has. All CK-Pro receiver sets come with; upper, lower, handguard, castle nut, ejection port assy, forward assist assy, and barrel nut installation tool. Upgrade your current platform, RUN COBALT!