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A thousandth of an inch is a derived unit of length in an inch-based system of units. Equal to 0.001 inches, it is normally referred to as a thou , a thousandth, or (particularly in the United States) a mil. The plural of ''thou'' is also ''thou'' (thus one hundredth of an inch is "10 thou"), while the plural of ''mil'' is ''mils'' (thus "10 mils"). Both words come from roots meaning "1000": "thou" from the English "thousand", which is from the Germanic root for 1000, and "mil" from the Romance root for 1000. The US Customary ''mil'' can be confused with the millimetre which is the standard meaning for "mil" or "mils" (plural), in British English and European engineering circles. This can cause problems with spoken dimensions or with those who are not familiar with alternative uses of the term. One US mil is approximately 1/40th of a millimetre at 0.0254 mm or 25.40 μm. ==Contexts of use== The thou, or mil, is most commonly used in engineering and manufacturing. 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 (30 mils in US) in thickness. * Manufacturing dimensions and tolerances, such as: * * In the manufacture of 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.) * * In the servicing of automobile engines (Typical examples include a spark-plug gap or ignition points gap.) * * The manufacture of printed circuit boards (PCBs) (although the component dimensions are now typically provided in millimetres) * * Tolerance specifications on hydraulic cylinders There are also compound units such as "mils per year" used to express corrosion rates.〔("Corrosion Rate Conversion" ), Corrosionist.com〕 A related measurement for area known as the circular mil, is based on a circle having a diameter of one mil. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Thousandth of an inch」の詳細全文を読む スポンサード リンク
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