This quick release coupling is used on the hydraulic brake line of your trailer. Since the master cylinder is on the extension tongue, the brake line must be disconnected to extend the tongue.
The original fitting that came with your trailer was similar but made from steel. Our replacement is all brass, eliminating the rust which caused early failure of the original fitting.
1) Although it is often possible to launch or retrieve your boat without extending the tongue, we advise against it. If your trailer is equipped with surge brakes, the master cylinder will often be under water. Since there is a vent hole in the cap of the master cylinder, you may introduce water into the system. This will cause the brakes to stop working almost immediately.
2) The male half of this quick release fitting connects to the back of the master cylinder, the female half connects to the flexible rubber hose. Both the male and female ends of the quick release fittings are threaded with 1/8" pipe thread.