The Noveske N4 Upper Receiver is a Mil-Spec carry handle upper made to fit all AR15/M16 M4 rifles and carbines. The Upper Receiver comes equipped with a shell deflector and forward assist, as well as a sight assembly. FeaturesNoveske Marked tear drop forward assistA2 adjustable rear sight (requires a NON-F marked front sight post if using a front sight post)Featuring anti-rotation interface with handguardReceiver designed to match the profile of Noveske 4th Generation handguardsPort door, rod and springN4 barrel nuts are threaded 1-1/4"x18TPI