XTS Micro Gas Block Black. 750 Gas Block MICRO-GB was created to be the perfect addition to your rifle. Specifications for XTS Micro Gas Block: Manufacturer: XTS Color: Black Fabric/Material: Aluminum Gas Block Journal Size-Diameter: .750 in Caliber: 5.56x45mm NATO Gun Model: AR-15 Additional Features: .750 Diameter Included Accessories: Dual set screws Gas tube roll pin Projectile Caliber: .223 Caliber Finish: Matte Features of XTS Flip-Up Posi Lock Front Sight Quick detachable front sight with adjustable A2 Square Post Assembly to fit all Picatinny/Weaver-style rails Equipped with locking retention thumb nut Clever and Robust Flip-up Posi-lockDesign Package Contents: XTS Micro Gas Block What firearm models does the manufacturer say XTS Micro Gas Block is compatible with? The manufacturer says that XTS Micro Gas Block is compatible with AR-15XTS MICRO-GB: Micro Gas Block Black