Our Special Edition: Liberty M4E1 Stripped Lower Receiver features a custom patriotic liberty shield emblem engraved on the magazine well of our popular M4E1 Lower Receiver. Markings Include Model "LBRTYM4" and "LTYM4-XXXXX" serial number range. Like all of our receivers, this product is machined to mil-spec dimensions and works with standard AR15 components. M4E1 Lower Receiver Improvements: 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). 1/16" Hex Key required for assembly. 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 AR15 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. Marked and milled to accept short-throw safety selectors, but will work with standard selectors as well. Includes: Stripped M4E1 Lower Receiver Nylon tipped tensioning set screw Threaded Bolt Catch Pin