This is the latest connector on the market. It is much smaller than our existing Quick Detach Couplers. If you are looking for a less bulky connector, then this is the way to go! Allows you to easily connect your HPA Engine Line from Wolverine, Polar Star, etc. to your HPA Line. Gun Side Tubing Size: 6mm Includes 1x Gun Side Connector Currently this coupler (Fosters Type) is the main type of connector that the Airsoft HPA industry utilizes.