Ken, the old Atco tank I have from a early 60s model has the same thread as the standard victa 2 stroke fuel tap - my alroh with tecumseh engine also has the same thread, so must be standard.
I believe 1/8 pitch, 1/4 inch size - but on 80% sure on that from memory
Ok thanks Tyler for the info I’ll have to find a Brass fuel tap from somewhere, I would have Brought one from George at Villiers parts in UK But the web site is down for some reason Cheers Ken