Cry Havoc Tactical 308 QRB Barrel Locking Plate Kit - Rifle Gas Tube. The 308 QRB Kit can only be used on Barrels with a maximum outside diameter of 1.200in and Free Float Hand Guards with a maximum width of 2.2in Also the QRB will add 1.5in to the length of your free floating hand guard. Specifications for Cry Havoc Tactical 308 QRB Barrel Locking Plate Kits: Manufacturer: Cry Havoc Tactical Gun Make: AR Platform Gun Model: AR-15 Color: Black Condition: New Last Chance: Yes Projectile Caliber: .308 Caliber Caliber: .308 Winchester Package Contents: Cry Havoc Tactical 308 QRB Barrel Locking Plate Kits Barrel Plate Gas Tube Cry Havoc Tactical 793888119819: 308 QRB Barrel Locking Plate Kit - Rifle Gas Tube