Geissele H1 Reliability Enhancement Kit Black. 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. Specifications for Geissele H1 Reliability Enhancement Kit: Manufacturer: Geissele Color: Black Fabric/Material: Carpenter 158 Carrier Material: Carpenter 158 Caliber: 5.56mm Gun Model: AR-15 Hand: Right Package Contents: Geissele H1 Reliability Enhancement Kit What firearm models does the manufacturer say Geissele H1 Reliability Enhancement Kit is compatible with? The manufacturer says that Geissele H1 Reliability Enhancement Kit is compatible with AR-15Geissele 05-492-H1: H1 Reliability Enhancement Kit Black