View source for Thou (length)

{{unit of length
|name=thou
|m=0.0000254
|accuracy=3
}}
A '''thou''', also known as a '''mil''', is a [[Units of measurement|unit]] of [[length]] equal to 0.001 [[inch]]es (a "milli-inch" or a "thousandth of one inch").  It is sometimes used in engineering and in the specification of:
* the thickness of items such as paper, film, foil, wires, paint coatings, latex gloves, plastic sheeting, and fibers; and
* manufacturing dimensions and [[tolerance (engineering)|tolerances]].

As the metric system became more common in the States, use of the term mil began to decline among technical users due to the possible confusion with millimeters.<ref>[http://www.unc.edu/~rowlett/units/dictM.html#mil Mil] at [http://www.unc.edu/~rowlett/units/ How Many? A Dictionary of Units of Measurement] by Russ Rowlett</ref><ref>[http://www.unc.edu/~rowlett/units/dictT.html#thimbleful Thou] at [http://www.unc.edu/~rowlett/units/ How Many? A Dictionary of Units of Measurement] by Russ Rowlett</ref>  However, the mil is still in common use in the United States for the thickness of plastic sheeting or bags.

Internationally, use of the thou is now generally deprecated in favour of the use of [[SI]] units of length such as the [[micrometre]]. In the United States, the mil/thou is still in use extensively in certain industries such as in the manufacture of [[Printed Circuit Board|printed circuit boards]] (PCBs).

The plural of ''thou'' is also ''thou'', e.g. a measurement of one hundredth of an inch is described as "10 thou". The ''th'' in ''thou'' is pronounced as in ''thousand'', {{IPAEng|θaʊ}}, unlike the pronoun ''[[thou]]'', {{IPA|/ðaʊ/}}, where the ''th'' is pronounced as in ''that''.

The plural of ''mil'' is ''mils''.

There is a related measurement for [[area]] known as the [[circular mil]], based on a [[circle]] having a [[diameter]] of one mil. Because of this relationship, a mil and a circular mil might be easily confused.

==Equivalence to other units of length==
1 thou is equal to:
* 0.001 international [[inch]]es (1 international inch is equal to 1,000 thou)
* 0.0254 [[millimetre|mm]], or 25.4 [[micrometre|μm]] (1 millimetre is about equal to 39.37 thou)

==Notes==
{{reflist|2}}

[[Category:Units of length]]
[[Category:Imperial units]]

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[[ja:サウ]]
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[[ru:Мил]]
[[zh:密耳]]
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