Thousandth of an inch
small unit of length in the imperial and US customary systems
A thousandth of an inch is a derived unit of length in a system of units using inches. Equal to 1⁄1000 of an inch, a thousandth is commonly called a thou (used for both singular and plural) or, particularly in North America, a mil (plural mils).
The words are shortened forms of the English and Latin words for "thousand" (mille in Latin). In international engineering contexts, confusion can arise because mil is a formal unit name in North America but mil or mill is also a common colloquial clipped form of millimetre. The units are considerably different: a millimetre is approximately 39 mils.
Contexts of use
The thou, or mil, is most commonly used in engineering and manufacturing in non-metric countries. For example, in specifying:
The thickness of items such as paper, film, foil, wires, paint coatings, latex gloves, plastic sheeting, and fibers
For example, most plastic ID cards are about 30 thou (0.76 mm) in thickness.
Card stock thickness in the United States, where mils are also called points.
Gauge (diameter) of strings in stringed instruments
Manufacturing dimensions and tolerances, such as:
In the manufacture of older automobile engines. A typical example is the thickness of the head gasket, or the amount of material to be removed from the head to adjust the compression ratio of the cylinders.
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This entry incorporates text from “Thousandth of an inch” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.