Includes: M4E1 Lower Receiver in Anodized Black M4E1 Threaded Assembled Upper Receiver in Anodized BlackM4E1 Lower Receiver Features: Threaded Bolt Catch Roll Pin - Allows for simple installation of the bolt catch and virtually eliminates the chance to damage the finish during installation (pin included). Integrated Trigger Guard - Eliminates the possibility of breaking the trigger guard tabs by integrating the trigger guard into the lower, creating a stronger more rigid platform to build upon. Upper Tension Screw - Allows users to fine tune the fit of the upper and lower receiver using a nylon tipped tensioning set screw inserted in the grip tang of the lower receiver. This provides a tight fit with any standard AR-15 upper receiver. Threaded Takedown Pin Detent Recess - Allows user to easily install the Takedown Pin detent and spring with the use of a 4-40 set screw (no more launching detents across the room). Increased Magwell Flare - Increased the flare of the magwell to aid in quick and efficient magazine changes.M4E1 Threaded Assembled Upper Receiver Features: New enhanced forging that gives the upper receiver a "billet look" Forward Assist and Dust Cover Already Installed M4 Feedramps .250 takedown pin holes Lazer engraved T-marks