This 9mm chambered 4.5 inch Modern Series Barrel is machined from 4150 Chrome Moly Vanadium steel with a QPQ Corrosion Resistant Finish and 1/2-28 x .400 full profile threads.Features: Designed to work with both Colt/RR and Glock style AR builds. Compatible with standard mil-spec uppers. There are also numerous dedicated 9mm upper options that work. Requires the use of a unique magwell conversion (Colt/Rock River style) with UZI mags or a dedicated 9mm lower with Glock mags. 9mm on an AR-15 platform operates by blowback and does not need a gas block or gas tube. Threaded 1/2x28 instead of 1/2x36 to give you greater versatility when choosing a suppressor. Integrated feed ramp and barrel extension. Since the barrel extension is an integral part of the barrel, the length stated is the true overall length. For example, an 11 9mm barrel has the same outer dimensions/length as a 10.5" 5.56 barrel. IMPORTANT: A standard 1/2x28 flash hider will not have enough clearance for a 9mm round to pass. Before installing a muzzle device, ensure a 9mm round will drop freely through the muzzle device bore.Specifications: Length: 4.5 Material: 4150 Chrome Moly Vanadium Profile: Straight Finish: QPQ Corrosion Resistant Gas System Length: Blowback Gas Block Journal: Blowback Gas System - No Gas Block Twist Rate: 1:10 inches Muzzle: 1/2x28 Threaded Weight: 8.1oz