In article ,
Andrew Gabriel wrote:
UNC -- Unified National Course
UNF -- Unified National Fine

I assume 3/6" is meant to be 3/16"?

Actually, the UK was partly responsible for these standards, but
didn't adopt them when they were finalised.

They were common on UK made cars until the mid '80s.

--
*Where there's a will, I want to be in it.

Dave Plowman London SW 12
RIP Acorn