Air Brake Gladhand - 2.5" scale (as used on narrow gauge rolling stock).
PLEASE CHECK MY REVISED VERSION!
Successfully tested!
Usable for vacuum, compressed air or liquid.
They hold 80 PSI with no leaks and the O-ring stays in place while uncoupling them till 40 PSI pressure (the pressure test was done, without using glue to fit the O-ring).
Use O-Ring (Dash 108, 50° Shore A, McMaster-Carr part number 1173N108) for sealing.
Nipple accept 5/16" ID flexible rubber hose.