It is actually my father that restores vintage cars. Some of his cars can be seen here...
(Mr Stevenson, you saw one when I came to see you last year, though the item is not for one of those)
Anyhow, I am younger than 40, so my measurements are in metric (though I can do English). It was just the micrometer I had to hand when I measured the threads, so I roughly translated it to english.
Mr Stevenson, as you are not too far from me (or my dad), (Kirkby-in-Ashfield), I have given him your details, so you may be getting a call from him pretty soon. He basically has a temperature guage and needs a nut for it.