Geissele Super Gas Stainless Steel Block w/SS Dowel Pin AR Platform 0.75in Diameter Black. Precision investment cast from 17-4 precipitation hardening stainless steel the gas block provides corrosion resistance and strength to withstand thousands of rounds and never let you down. The included instructions cover the standard set screw installation method as well as Geisseles own Bombproof Installation. The bombproof installation uses an included coil pin to lock the gas block in place on the barrel so that it will never slide or twist under any operating conditions. Additionally the Super Gas Block comes with a SS dowel pin that can be used to effortlessly line up the SGB to Geissele CHF barrels to ensure a perfect alignment with the gas port. Specifications for Geissele Super Gas Stainless Steel Block w/SS Dowel Pin: Manufacturer: Geissele Color: Black Fabric/Material: Steel Gas Block Journal Size-Diameter: .750 in Size: Compact Caliber: 5.56x45mm NATO .223 Remington Gun Make: AR Platform Gun Model: AR-15 Finish: Black Nitride Package Contents: Geissele Super Gas Stainless Steel Block SS Dowel Pin Bombproof Coil Pin 2 Set Screws Gas Tube Coil Pin Stainless Steel Barrel Alignment Pin What firearm models does the manufacturer say Geissele Super Gas Stainless Steel Block w/SS Dowel Pin is compatible with? The manufacturer says that Geissele Super Gas Stainless Steel Block w/SS Dowel Pin is compatible with AR-15Geissele 05-807B: Super Gas Stainless Steel Block w/SS Dowel Pin AR Platform 0.75in Diameter Black