Thousandth of an inch

A thousandth of an inch is a derived unit of length in a system of units using inches. Equal to 11000 of an inch, a thousandth is commonly called a thou /ˈθ/ (used for both singular and plural) or particularly in North America a mil (plural mils).

Thousandth of an inch
1 thou in ...... is equal to ...
   imperial and US customary systems   0.001 in
   SI units   25.4 μm

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.[1] The units are considerably different: a millimetre is approximately 39 mils.

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