John Rumm wrote:
Roger Chapman wrote:

http://wiki.diyfaq.org.uk/index.php?...fying_a_thread


I must have missed the original thread or I would have spoken up at
the time as I think the quote below is more than a little misleading

"Once you've ruled out metric then the job gets easier. Imperial
threads don't generally have variants. UNC is the standard imperial
coarse and UNF the standard imperial fine. On old machinery you might
come across Whitworth which is an early coarse or its fine equivalent
BSF."

I wouldn't class UN threads as Imperial. While I don't care a toss
about upsetting the Merkins I think they had a bigger hand in that
introduction that the Brits.

On old British machinery Whitworth was the norm. My first socket set
bought in 1964 was both AF and Whitworth and I think Whitworth could
still be found on some cars actually manufactured in the 1960s
although my car at the time was a 1952 Riley 2.5 and memory fades (or
at least my does) as to what was or was not current after such a long
time.

Oh yes and BSP is of course a Whitworth thread.

I won't attempt to edit the FAQ. Someone is bound to object to my
intervention on principle so I leave it to others to correct should
they think it important enough.

That is what the wiki is there for - so please *do* edit it. Since I
have posted it as transcript of Dave's original post, it would be unfair
to change his words, however adding another section to the bottom as a
commentary seems entirely reasonable. I have added an "Additional
Comments" section so that you can ;-)

That would require me to find evidence that my memory wasn't playing
tricks on me. (So far I seem in the clear). It is amazing what you can
find on the web if you really try. :-) I searched for Whitworth for
starters and didn't really get much joy other than the year it was
introduced - 1841. Then 'ISO Inch' and eventually came upon:

http://www.sizes.com/tools/thread_american.htm

Of which the paragraph below is an extract.

"The differences between American and British thread forms became a
painful problem during the Second World War, especially in manufacturing
and repairing airplane engines. In 1948 representatives of Britain,
Canada and the United States agreed on a Unified Standard."

Seems ironic to me that as late as 1948 (see link) the Merkins were
still in favour of flat bottomed screw threads and all that associated
nastiness with stress raisers.

I have generally steered clear of the wiki so not sure of what is
acceptable but ISTM that the link above is all that is really needed for
unified threads.

I have yet to search out BSP but I have a reference book that states;

"British Standard pipe threads are recognised by ISO and are maintained
in the inch system with fractional designations for pipe joints."
Nevertheless when it comes to the detail apart from threads per inch and
nominal bore all dimensions are given in mm.

The other important point about BSP is that it can be found in both
taper and parallel form.