Galletto copper oil pipe - Whitworth?

I’m having a bit of a head scratch with my Galletto 175. It’s a restoration from a complete basket case and although most of the bits where in said baskets, only one of the oil pipes was there. The odd thing is, it would seem to be a non metric fitting. The existing return pipe is 5/16" with 7/16" banjo nuts. I’ve dug out and old thread gauge and measured the threads on the nut that I have and it appears to be whitworth 20 1/4 (whatever that means - I only do metric!)

I reckon I can solder a feed pipe up but does anyone think the Whitworth / UNF fitting is likely? 7/16 equates to M11 ok but a thread of 1.25 is definitely wrong, so why would Italians use Imperial fittings?

If anyone knows of a company who make up these pipes, I’d be much obliged.

Ta. Nick. :unamused:

BSP? BSP threads are pretty universal, even in otherwise Metric environments.

BSP (British Standard Pipe Thread) is pretty standard worldwide for pipework and is of Whitworth thread form. It can be parallel or taper in form. 1/4" BSP thread has 19 TPI and an outside diameter13.157mm (0.518")
The metric nomenclature for it is R1/4, Rc1/4, & Rp1/4. Where R is a taper male thread, Rc is a taper female thread and Rp is a parallel thread (male or female).
R/Rc combination seals on the thread, R/Rp seals on the thread and Rp/Rp requires a sealing face as it does not seal on the thread. It is over 8 years since I retired but I think I have remembered the information correctly.