The new XS Scuba First Stage Quick Disconnect allows a diver to quickly change to a different hose length. This is especially useful for hookah divers (boat bottom cleaners) as well as other application. The complete QD is required for one set up, but if you have multiple second stage hoses you will need one female coupling (included) connected to your first stage and multiple male fittings (AC999) for each of your additional second stage hoses, so you can plug them into your first stage female coupling. Lock-down screw to prevent accidental disconnection with one end male 3/8"-24 threaded, the other end is female 3/8"-24 threaded. QD is manufactured from durable chrome plated brass for low maintenance and long life. Coupling is factory cleaned, has Viton O-rings, and is designed for low pressure only below 200 psi (13.8 bars).