The Jack - Gen2 features includes a threaded bolt catch pin, reduced weight and improved styling. It is machined top to bottom from 7075-T6 aluminum with an oversized and integral trigger guard, beveled magazine flare, and a Multi caliber mark. The Jack is fully compatible with all mil-spec internal parts and other aftermarket mil-spec upper receivers, and GI standard issue magazines as well as PMags. NOTE: Requires a lower parts kit, buffer & stock of your choosing to complete.