Metric or Decimal..accuracy?

How about M1.2 ?


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Nick Müller
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I do voluntary work for a charity - we custom make aids for disabled people. One case a few years ago was particularly complex and involved the collaboration of several people, one of them being a draughtsman who produced the drawings using AutoCad. The dimensions were metric and displayed to an accuracy of 0.001mm - 20x finer than we could work to. The trouble was, he committed the cardinal sin and decided to modify a dimension manually, which resulted in one part being 1 inch too short, but accurate to 0.001mm.

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What about 1.1, 1.2, 1.4, 1.6, 1.8, 2.2, 2.5, 3.5, and 4.5? They are all standard metric sizes, available as both coarse and fine threads.

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Here I were little incorrect - but are those real "four decimal places"? Or maybe it is M2.2-0.35 which is "four decimal places"? And anyway - how many "regular garden hoses" with this size of thread do you know about?

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russian designer

Umm, Arcady? You missed the point of the story, but I'll explain it anyway:

There are lots of standard "US" threads/connectors/nominal sizes which do not make sense if directly translated to metric. Ever try to write down the spec for "three-quarter inch conduit" in metric? Or for "2x4 lumber" in metric? Hint: you DO NOT take the nominal US measurements.

Works the other way around too. I'm sure I could specify a M5x0.8 thread in US measurements but it'd look like "0.19685 inch major diameter and 31.75 tpi" and you will have zero success if you go into a hardware store with that sort of spec. Worst case is they decide that I really meant a 10-32 screw which is NOT gonna go in more than a couple of turns!

What I think is a hoot is when tourist books are rewritten into the "non-natural" units and then it's translated back, gaining a couple of extra decimal places at every step. For example "over 2 kilometers" in the metric original becomes "over 1.24 miles" which then becomes "over

1.9958 kilometers" in the doubly translated!

Anyway, now that's all done, go back and read the punch line (which you handily deleted.) The point of the story is that you if you express metric tooling in inch sizes, or inch tooling in metric sizes, you probably aren't gonna find anything off the shelf.


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or M2.5x0.45 ?

Enjoy, DoN.

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DoN. Nichols

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