|The SM-1 Modular Barrel System is the most precision manufactured barrel available today. Its unique 3-piece Stainless & Aluminum design incorporates a barrel-sizing sleeve system that's way ahead of its time! Simply use the included Barrel Tool (or any adjustable open-ended wrench) to help you unscrew the 5.5inch threaded choke from the stainless steel Sizing Collar, and you can re-size your barrel in seconds! Comes with 4 insert sizes: .679, .683, .686, and .689. The Aluminum Barrel Front is honed to a micro-polished .692. Paintball experts all agree that the key to accuracy is improving ball to barrel fit, and this barrel system, will help you achieve your goals! Measures 14in long.