This page :- http://airpowered.co.uk/aircouplingidentification.htm - may help resolve the confusion. Your long one is "real" PCL (the original makers initials) and the one I'd advise you to standardise on as its certainly the easiest to find in the UK and still very common on the continent. Its rare to find badly made ones that don't fit properly. Short one is supposed to be Euro but some suppliers call them PCL-Euro which is very confusing (yes Draper this means you). XF couplings look the same as Euro to a casual glance. No idea if they are interchangeable as I routinely bin anything that isn't PCL although the higher airflow of Schrader ones is sometimes tempting but am I gonna change 20 or so sets over. Nope! These pages may be of interest :- http://www.pclairtechnology.com/products/couplings-adaptors/interchange-range/ - and :- http://www.pclairtechnology.com/products/couplings-adaptors/ .

Not impressed by euro style couplings on cheap imports as quality and size is all over the place. Had to change out some for other folk when the accessories in a one box compressor kit accessories didn't fit the line supplied! To make matters worse the threads were Admiralty size and TPI with SAE style 60° threads. Which took a deal of tracking down as I've not seen a genuine Admiralty thread out in the wild of 40 years and that kit was old then so I'd completely forgotten the standard existed. Shame its fallen out of use as it's handy for odd sized stuff.

Should be BSP thread on the end of adapters. Usually taper on a PCL male nose. Equipment tapped holes tend to be parallel so you need a male female adapter for the taper thread. Euro style is often parallel to easily screw direct into kit. Have run into cheap stuff with a sort of half'n half tapered - parallel thread which fits neither unless gobbed up with lots of PTFE tape.

I really need to charge more for sorting out "friends" cheap crap. Then maybe they'd listen and buy a bit further up market.

Clive