Chris Hodges wrote in message o.uk...

3/4" NPT is 14TPI, while GHT (always 3/4") is 11 1/2 TPI.

Very weird.

The last one I connected, I cut the ends off the hoses and fitted
3/4" BSP barbed hose connectors with Jubillee clips. I heard nothing
more about it, so assume it all worked. I chucked the OEM's US chunky
brass hose connectors in the box of 'potentially useful' bits,
expecting that I'd one day find a matching thread that could use them.
I never did, they're probably still there.