For me, a Russian, born and raised with metric system, learning about these things had been / is a very curious topic!
When it comes to machining, I usually read the Model Engineer forum (UK) and the Practical Machinist forum (USA).
I don't recall people on either of the forums using "mil", at least not often (or perhaps I haven't noticed)?
The term "thou", though, comes up very often, as well as "tenth".
The funny thing is, I have a 1966 USA book "Fundamentals of Dimensional Metrology" by Ted Busch.
The book has a rather thoughtful discussion on pros and cons of the metric system and the decimal inch system.
It talks about an upcoming (at the time) Decimal Inch standard:
Quote:
- In 1959 the American Standards Association (ASA) and American Society of Tool and Manufacturing Engineers (ASTME) decided to jointly urge greater use of the decimal inch. ... The committee formed for this purpose was known as ASA Sectional Committee B87. ... This proposal, known as ASA Standard B87, is being considered for approval at the time of this writing.
Curiously, outside of this book, I was not able to find some information about it's history or fate!
Some more quotes:
- The "thousandths" division of the inch is one of the most useful. Unfortunately it is a tongue twister, hard to spell, and easily confused with "thousand". Slang was already shortening it to "thou" which is even more ambiguous. Mil was a much better choice. It is similar to the official international prefix "milli" meaning thousandths. The prefix "mil" is from Latin and widely used by non-technical people. And it is short enough.
- In practical work one tenth of a thousandth of an inch is frequently encountered. Alas, it acquired the most unfortunate name possible, the "tenth". Tenth of what? The resulting mistakes that have been made are legend. Furthermore, in the opinion of many who have studied the metric system, if it teaches anything, it is that units that vary only by a factor of ten are an open invitation to trouble. Therefore, this interval is skipped in the decimal-inch system. One-tenth part of one thousandth inch is simply point one mil (three syllables) or one-hundred mike (four syllables).
The book suggests, though, that one ten thousandth of an inch is such a useful and needed unit, that it suggests using "tenth mil" to remove ambiguity.
- The next unit is one millionth of an inch. Again the word was chosen for much the same reason as was mil. "Micro" of the international prefixes was an obvious choice. In the decimal-inch system it is simplified to mike.
Regardless of using a standard that seems to not had gained enough traction, this book is a pretty great (and even entertaining!) read.
Funnily, I've never encountered "mike" in contemporary usage on the machinist forums (I've heard micro-inches). Everyone seems to say "tenth" or "thou".
FYI: Russian machinists measure in microns or sometimes in 0.01 mm units - called §ã§à§ä§Ü§Ñ (sotka), literally a hundredth, = 1/2.54 of a "thou" or a "mil".
If someone has a more or less recent USA book on metrology, what kind of units it suggests?
I wonder if UK metrology books still mention decimal inches, considering that UK had *mostly* been metric for a long time now?
--Gene
