The Geissele Reliability Enhancement Kit includes the Geissele Reliability Enhanced Bolt Carrier Group (REBCG) and the Geissele Super 42 Braided Wire Buffer Spring & Buffer in your choice of H1, H2 or H3 configuration for 5.56mm AR-15 pattern rifles. The Geissele REK is the culmination of a many years of extensive testing and fine tuning to bring you the most reliable operating system upgrade you can make to your carbine.Manufactured in Geissele's state-of-the-art manufacturing facility in North Wales, PA. The REBCG is a 5.56mm full-mass, full-auto rated M16/M4 bolt carrier group. The carrier is machined from mil-spec 8620 steel, and features a properly torqued and stake Mfg: Geissele Automatics Llc