Editing Unified Thread Standard (section)

==Basic profile==
[[File:ISO and UTS Thread Dimensions.svg|thumb|320px|The basic profile of all UTS threads is the same as that of all [[ISO metric screw thread]]s. Only the commonly used values for {{math|''D''<sub>maj</sub>}} and {{mvar|P}} differ between the two standards.]]

Each thread in the series is characterized by its major diameter {{math|''D''<sub>maj</sub>}} and its pitch, {{mvar|P}}. UTS threads consist of a symmetric V-shaped thread. In any plane containing the thread axis,  the flanks of the V have an [[Thread angle|angle]] of 60° to each other. The outermost {{frac|1|8}} and the innermost {{frac|1|4}} of the height {{mvar|H}} of the V-shape are cut off from the profile.

The major diameter {{math|''D''<sub>maj</sub>}} is the diameter of the screw measured from the outer edge of the threads. The minor diameter {{math|''D''<sub>min</sub>}} (also known as the root diameter)  is the diameter of the screw measured from the inner edge of the threads. The major diameter may be slightly different from the shank diameter, which is the diameter of the unthreaded part of the screw. The diameters are sometimes given approximately in fractions of an inch (e.g. the major diameter of a #6 screw is 0.1380&nbsp;in, approximately {{nowrap|1={{frac|9|64}} in =}} 0.140625&nbsp;in.

The pitch {{mvar|P}} is the distance between thread peaks. For UTS threads, which are single-start threads, it is equal to the [[lead (engineering)|lead]], the axial distance that the screw advances during a 360° rotation. UTS threads do not usually use the pitch parameter; instead a parameter known as [[threads per inch]] (TPI) is used, which is the [[Multiplicative inverse|reciprocal]] of the pitch.

The relationship between the height {{mvar|H}} and the pitch {{mvar|P}} is found using the following equation where {{mvar|θ}} is half the included angle of the thread, in this case 30°:{{sfnp|''Machinery's Handbook'' 29|2012|p=[https://archive.org/details/machineryshandbo0000unse_f4b1_29edition/page/1806/ 1806]}}

<math display=block>\begin{align}H &= \frac{ {P}}{2\tan \theta} = \frac{ \sqrt 3 }{2} \cdot P \\[.5 em]
&\approx 0.866025 \cdot P\,.\end{align}</math>

In an external (male) thread (e.g., on a bolt), the major diameter {{math|''D''<sub>maj</sub>}} and the minor diameter {{math|''D''<sub>min</sub>}} define {{em|maximum}} dimensions of the thread. This means that the external thread must end flat at {{math|''D''<sub>maj</sub>}}, but can be rounded out below the minor diameter {{math|''D''<sub>min</sub>}}. Conversely, in an internal (female) thread (e.g., in a nut), the major and minor diameters are {{em|minimum}} dimensions, therefore the thread profile must end flat at {{math|''D''<sub>min</sub>}} but may be rounded out beyond {{math|''D''<sub>maj</sub>}}. These provisions are to prevent any interferences.

The minor diameter {{math|''D''<sub>min</sub>}} and effective pitch diameter {{math|''D''<sub>p</sub>}} are derived from the major diameter and pitch as:

<math display=block>\begin{align}
  D_\mathrm{min} &= D_\mathrm{maj} - 2H\cdot\frac58 = D_\mathrm{maj} - \frac{ 5 {\sqrt 3}}{8}\cdot P \approx D_\mathrm{maj} - 1.082532 \cdot P \\
    D_\mathrm{p} &= D_\mathrm{maj} - 2H\cdot\frac38 = D_\mathrm{maj} - \frac{ 3 {\sqrt 3}}{8}\cdot P \approx D_\mathrm{maj} - 0.649519 \cdot P.
\end{align}</math>