Fits inside the VSR10 rifle. Works with Tokyo Marui and clone VSR10 shorter GSpec airsoft sniper rifles. This is a 6.03 inner barrel diameter, so it allows for less jams and tolerances than the 6.01mm. A very popular choice as an alternative to the Prometheus. One piece high grade metal machined. Precision smooth inner bore with nickel plating. This inner barrel is an upgrade to improve your gun's performance, accuracy, FPS, and range compared to stock gun barrels.