Greetings Kees!

 KvE>>>  Yes great, the same inch based spanners, but with Witworth tread,
 KvE>>> a different pitch from the inch based UNF.

 RW>> But the same as the 'inch based UNC' threads with, as you point out,
 RW>> a different thread angle.  50° vs 60°...

 KvE>>> There was another difference as well, the angle of the thread
 KvE>>> flanks.

 RW>> I don't understand 'thread flanks' - Would you be referring to pitch
 RW>> angle? As in the example above.

 KvE>  I don't know the different treads and their specifics by name. This
 KvE> is all from memories of the mid sixtie. But indeed one was a
 KvE> difference in thread angle as you mention above.

Yes, my 1961 Machinists Handbook shows the specifics for each type.

 KvE> The was also a difference of one tread/inch between two standards.

SAE has two 'well known' standards of NC and NF, one being a course thread
and the other a fine thread. There are others as well, most of which are
used in different industries as in NEF or National Extra Fine threads as
used in microscopes as well as telescopes.

 KvE> To some extent these were echangeable as well.

To some extent, yes.

 KvE>  At the time I was an intern at engine revision company. Some of the
 KvE> engines were british made other were from US made draglines. Both
 KvE> used "exotic" threads. The machinery I used in my professional life
 KvE> was German built, so that was all metric.

Most thread making machines are capable of making any thread pitch, the
rest is in the operator of the machine. I have a small hobby lathe that
can produce metric threads, but with some gear changes, it will also make
SAE threads too. The lathe was made in China and I bought it while in an
emergency situation and figured to buy something bigger and better later
on.

 KvE>  Pipe thread has not been converted to the metric system, apparently
 KvE> the pipes did not either.

Pipe threads have been converted to British and metric. When Michiel was
telling about his plumbing job, the fittings he used were sold to him as
metric, but the actual measurements are still in SAE and then converted.

    Have a day!

         R\%/itt - K5RXT

... WH advisor says that voters are stupid; slighting the majority of
    Democrats (liberals) who voted for the O'bama, not once, but twice.

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