Hi Mark
Thanks for your advise. The thread on the 28 does appear very fine indeed, so I'm guessing it's 2mm. While the MPCC does look a little wider it's certainly not 5mm. I can confirm that the MPCC isn't cross threaded, as it has a flange which is removed to expose the thread and the action is smooth.
That only leaves the UWAN
I don't have any 2" filters but I'll try and get my hands on one to test. It's brand new of course, direct from the manufacturer.