# Confusing Terms "mil" Vs. "thou"......



## brino

Does anybody know where the term "mil" meaning thousandths of an inch came from?

I still hear it used in things from printed circuit board manufacture to mechanical design.

However, I have seen people that have been schooled totally in metric say "mill" to mean millimetre!
I have to stop them and ask what they really mean...maybe the pronounce the extra "L", but I cannot hear it!!

Personally I HATE the term "mil" as I do NOT believe that it is universally understood.
Does it mean "thou", "millimetre", millionth of an inch? what?

-brino


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## John Hasler

"Mil" comes from the Latin _mille_ which means thousand.


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## Tony Wells

It's been in common use as 1/1000" for a while now in plastic film thickness (garbage bags, etc.) and in measuring wet film thickness in paint as well as plating thickness. If today, kids are using it as millimeter, I believe they are incorrect in doing so.


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## RJSakowski

brino said:


> Does anybody know where the term "mil" meaning thousandths of an inch came from?
> 
> I still hear it used in things from printed circuit board manufacture to mechanical design.
> 
> However, I have seen people that have been schooled totally in metric say "mill" to mean millimetre!
> I have to stop them and ask what they really mean...maybe the pronounce the extra "L", but I cannot hear it!!
> 
> Personally I HATE the term "mil" as I do NOT believe that it is universally understood.
> Does it mean "thou", "millimetre", millionth of an inch? what?
> 
> -brino


The term mil meaning .001" has been around as long as I can remember.  It may be more significant as a reference to thickness.  It has apparently been in use since the 17th century.  
I have never heard it used referring to millionths.  Microinches are used instead.

The term mill referring to 1mm in the metric system is most likely slang similar to using thou for thousandth.  I had never run into that usage in educational experience.  A few years back, I did have some miscommunication with an engineering firm when specifying some tolerances.  Since then, I have been careful to specify thousandths or .001".

To confound the issue, mil is also used to refer to 1/6400th of a circle (.056 degrees), used mostly in reference to artillery angles; orally in reference to 1/1000th of a liter or ml, although I have never seen it spelled as mil; as a monetary unit equal to 1/1000th $ in the US; and in Sweden as 10km. Also used as a rate equal to .1% as in tax rate and finally, as an acronym for mother in law.

Now, aren't you glad that you brought it up?


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## brino

RJSakowski said:


> Now, aren't you glad that you brought it up?



Absolutely!

You also made me remember another instances.....circular mils when referring to to wire cross-sectional area, where again it's really "thou".

-brino


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## John Hasler

brino said:


> Absolutely!
> 
> You also made me remember another instances.....circular mils when referring to to wire cross-sectional area, where again it's really "thou".
> 
> -brino


The "circular mil", often stated as MCM for thousand circular mils, has to be one of the ugliest units of measure ever invented.


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## extropic

brino said:


> snip
> Personally I HATE the term "mil" as I do NOT believe that it is universally understood.
> snip



I'm pretty sure that there is no term that is universally understood. Universal understanding is as rare as perfection.


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## uncle harry

John Hasler said:


> The "circular mil", often stated as MCM for thousand circular mils, has to be one of the ugliest units of measure ever invented.




I never really cared for the expression FPF (furlongs per fortnight).  Hard to convert !


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