Thou (length)

Thou (length)
1 thou =
SI units
25.4×10^−6 m 25.40 μm
US customary / Imperial units
83.3×10^−6 ft 1.00×10^−3 in

A thou (pronounced /ˈθaʊ/) also known as a mil or point, is the verbalized abbreviation for "thousandth(s) of an inch." It is a unit of length equal to 0.001 inch.

The plural of thou is also thou; e.g., a measurement of one hundredth of an inch is written as 10 thou, while the plural of mil is mils. The th in thou is pronounced as in thousand, /ˈθaʊ/, unlike the pronoun thou, /ðaʊ/, where the th is pronounced as in that.

The introduction of the thou in 1844 is generally attributed to Joseph Whitworth.[1]

In the United States, the usual term has been mil, whereas thou has been more common elsewhere.[2][3]



The thou (or mil in US) is sometimes used in engineering, machining, 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 tolerances.
  • 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)
  • tolerance specifications on hydraulic cylinders.

There are also compound units such as "mils per year" used to express corrosion rates.[4]

There is a related measurement for area known as the circular mil, based on a circle having a diameter of one mil.

In machining

In machining, it is common to work to positions with accuracies of one thou, several thou, or even a fraction of a thou. One tenth of a thou is one ten-thousandth of an inch (0.0001"). Because machinists often think in terms of the thou as the "base unit" in their context, it follows that they call 0.0001" "one tenth", meaning "one tenth of a thou". Machining "to within a few tenths" is usually considered very accurate, with few and special exceptions. This level of accuracy is more common in Tool and die work than in production or MRO work.

The metric analog of thou and tenths [referring back to the inch] is hundredths and microns [referring back to the millimeter]. (The name "micron" is now deprecated by SI in favor of "micrometre", but "micron" is still commonly heard in industry.) This metric "scale of thinking" represents slightly smaller distances than does the corresponding inch-based scale of thinking (thou and tenths). Therefore, machining in metric units is occasionally preferred to working in thou for extremely precise work. But there are other factors involved in deciding which one is used in any particular case, and this difference rarely matters. On CNC machine tools, all linear motion is based on the minimum increment of the control system, which is either one "micron" (one micrometre, 0.001 mm) or one "tenth" (0.0001"). The metric standard widely prevails today, both because it is physically smaller and because SI prevails in measurement worldwide, and globalized manufacturing uses ISO standards as its benchmarks. But the control allows the user to work in either system, because the computer does the unit conversions automatically (rounded to the nearest minimum increment).

mil versus thou

In the United States, the usual term has been mil, but as use of the metric system became more common thou has begun to replace mil among some technical users to avoid confusion with millimeters.[2][5][3]

Equivalence to other units of length

1 thou is exactly equal to:

  • 0.001 international inches (1 international inch is equal to 1,000 thou)
  • 0.0254 mm, or 25.4 μm (1 millimeter is about equal to 39.37 thou)

The most common thickness of most plastic ID cards, 30 thou (30 mils in US), is equal to 0.03 inches (0.76 mm).

See also


Wikimedia Foundation. 2010.

Игры ⚽ Нужна курсовая?

Look at other dictionaries:

  • Thou (disambiguation) — Thou is an archaic second person singular pronoun in English.Thou may also refer to: * Thou (unit of length) * Thousand * Thou., a reference to French botanist Louis Marie Aubert du Petit ThouarsIn geography: * Le Thou, a commune of Charente… …   Wikipedia

  • Thou Shalt Suffer — is a black metal band from Norway. The group, a precursor band to Emperor, features Ihsahn s trademark keyboard melodies combined with various death metal elements, including vocal stylings. When the group broke up due to the formation of Emperor …   Wikipedia

  • Thou Art Lord — are an Athens based black metal band, formed in 1993.The line up consists of former or current members of Greek extreme metal bands Rotting Christ, Necromantia, and now former musicians from Septic Flesh. The band s first release was an EP/split… …   Wikipedia

  • Thou Shalt Not (album) — Infobox Album | Name = Thou Shalt Not original Broadway cast recording Type = Album Artist = Harry Connick, Jr. Released = flagicon|US June 18 2002 Recorded = Genre = Cast album Length = 1:17:24 Label = Papa s June Music Producer = Tracey Freeman …   Wikipedia

  • Thou Shalt Always Kill — Infobox Single Name = Thou Shalt Always Kill Artist = Dan Le Sac Vs Scroobius Pip from Album = Angles B side = Released = flagicon|United Kingdom April 16, 2007 Format = CD Single Recorded = Genre = Length = 5:19 Label = Lex Records Writer =… …   Wikipedia

  • Thou Art in Heaven — Infobox Single Name = Thou Art in Heaven Cover size = Caption = Artist = Mike Oldfield from Album = Tres Lunas A side = B side = Released = start date|2002 Format = CD Recorded = Genre = Chillout Length = Label = Warner Music UK Writer = Mike… …   Wikipedia

  • thou — 1. pronoun /ðaʊ/ you (singular informal) 2. verb /ðaʊ/ a) To address (a person) using the pronoun , especially as an expression of familiarity or contempt. One service more, Sahib, since thou hast come so opportunely, said Lalun. Wilt thou – it… …   Wiktionary

  • Thou Shalt Not Fall — Infobox Album | Name = Thou Shalt Not Fall Type = studio Artist = G Tom Mac Released = 2007 Recorded = Titan Recording, Los Angeles Genre = Rock Length = Label = Edge Artists Producer = Gerard McMann, Tony Silver Reviews = Last album = G Tom Mac… …   Wikipedia

  • Thou Shalt Not Kill (Spooks) — Infobox Spooks episode episode name = Thou Shalt Not Kill writer = David Wolstencroft director = Bharat Nalluri script editor = producer = executive producer = series = 1 episode = 1 length = 59 minutes UK date = US date = preceding = N/A… …   Wikipedia

  • O Brother, Where Art Thou? (soundtrack) — O Brother, Where Art Thou? Soundtrack album by Various Artists Released December 5, 2000 (2000 12 05) …   Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”