Double Shut-Off Valves in both coupler and plug help to minimize fluid loss when connecting or disconnecting fluid lines, and prevent loss of fluid once disconnected. The valve in the plug is activated by a pin in the coupler when both are connected. When disconnected, the valves in both coupler and plug are shut, thus eliminating leakage from either end. Smaller than your thumb, but when it comes to capacity, our miniature Quick Connectors beat many other couplers. Hand-operated Quick Connectors are great for use with small air tools, dental equipment, test equipment and in automation.