Dom wrote:

Until as recent as a few years back, the international measurment
standard was a platinum bar with 2 X's engraved on it, preserved in
Paris. The X's are 1000mm apart. This bar is the standard that all
measurements were defined from, with the Inch being defined as
25.4mm. Now the standard length is calculated from the distance light
travels in a vucuum. Tradition tells us that the inch was one twelth
of the length of Hercules foot.

It is interesting to note that while people may argue against
metrification, in reality the Imperial system is now derived from the
Metric system.

This year the BSPF and BSPT thread standards have now been given a new
"Metric" Designation ISO Rc Series (Taper) and ISO G Parallel
Series. They are still designated with fractions and TPI, but have
been incorporated into SI standards. This is a good example of
"Inchification". Hope this makes some of you Yankees feel a bit
better.

Not likely as those standards are British and not US. US thread
standards differ from British in TPI for most sizes and the included
angle of the thread.


Cheers from Down Under

Dominic.