Fill hose question

That type of union needs to marry up with a fitting with a reverse cone shaped base. The loose nut on the hose side clamps the two sealing surfaces together a bit like some high-pressure portable propane camping stoves. If you are looking for something for your rig, have a look at these. https://www.aliexpress.com/item/PCP-Airforce-Pneumatics-Air-Pump-High-Pressure-Nylon-Hose-50cm-100cm-150cm-200cm-Hose-with-Quick/32853214021.html?spm=a2g0s.9042311.0.0.694d4c4dUlgmo1 I've got a feeling that the type of hose you 

are looking at, is the type that bubblerboy was looking for, for his Daystate compressor a few weeks ago.