Shuffling forward, imperial or Metric, it’s all maths, the power comes from going deeper past the decimal point.
Anthony,
It is not
just math, it is
design as well. The
ABC (American-British-Canadian) standards promulgated for WWI established quite a few well
designed criteria. A (now Unified National or)
UN Fine thread has 15% greater tensile & shear properties than a
UN Coarse thread and a
UN Extra-Fine thread has 15% greater tensile & shear properties than a
UN Fine thread. That was a
criteria set by the
ABC Joint Industrialization Council back in 1912!
In the ISO (metric) thread system, an
ISO Fine thread has a (roughly)
3% in tensile or shear properties than an
ISO Standard (or Coarse) thread. Further, an
ISO Standard thread
must be used with a threaded insert in low-shear materials whereas a
UN Coarse thread was
designed to work with low-shear materials. The ISO system
began being defined 35 years
after the
ABC system (which, in turn became:
ASA/
CSA and
UN systems).
I was able to tabulate relative male- and female-thread shear areas (i.e. pull-out strengths) for
every UN thread from #0 (.060 major diameter) through 1.500 inches along with a lot of other useful data in just 5 total pages. Until the
allowance & tolerances for metric threads are unified, I shan't even attempt that task. My best estimate is that such an effort today would require more than 125 pages to tabulate.
And you do
not want to get me started on that most useless of units, the
Newton!