[sdiy] Metric OT rant

jorgen.bergfors at idg.se jorgen.bergfors at idg.se
Mon Aug 12 08:08:42 CEST 2002


>The only bicycles that I know of that are all
metric are French.

Yeah, and in the english "system" there is a special cycle thread for
bicycles. Which is not compatible with standard pipe thread or Whitworth,
UNC, UNF, UNEF for that matter.
By the way, do you know that a 2" pipe thread does not have the measure 2"
anywhere? It was originally that the 2" pipes had an inner diameter of 2",
but nowadays, with improved steel quality, the pipes are thinner. So the
inner diameter is larger than 2" (they didn't want to change the thread
standard, for obvious reasons).
So you see what a mess the "english" system really is?
If not, try to figure out why a 1/2" nut does not fit on a 1/2" bolt. Hint:
the nut is Whitworth and the bolt is UNC, or viceversa.

By the way, do you know how an inch is defined? It is defined as 25.4
millimeters!
It was defined by the swede C. E. Johansson (http://www.cej.se/), who
manufactured precision measurement equipment. He found out that there
didn't exist any really precise definition for the inch. The americans had
different competing definitions, which weren't precise enough anyway. So he
just decided that an inch was 25.4 millimeter, without telling anyone. When
the americans found out, it was too late, as many of them, had already
bought Johansson's equipment.

/Jorgen
Sweden





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