Just gone through a similar scenario but i needed a new air line .
Seems most use the same thread but iwata and a few others use a different one 1/8 bsp i think .
You can get adapters off ebay for most guns although i have a realmcheap gun that uses fittings that are around 5 mm , it is cheap junk but good for priming so i will adapt it to my other fittings .
Any thoughts on paasche guns ?
I have a cheap diaphragm compressor and want to add a small air tank to it , possibly from a small fire extinguisher or gas bottle .
i only use it for my model engines or static models like 1:72 scale models but it seems to work well .