I'm refitting a monblock tap which originally had rigid tails - no idea
of make/model. I removed the rigid tails and found a 12mm thread on
them so I bought 12mm tails from Screwfix. Thing is, the new tails seem
to have a higher TPI on the threads and won't go in. I don't think I
could even bodge it in satisactorily.

So, anyone got any ideas if there are just a few 'standards' for this
sort of thing or am I better sticking with rigid tails or buying a new
tap?