Unified Thread Standard

From Academic Kids

The Unified Thread Standard (UTS) specifies the standard thread form, series, class, allowance, tolerance, and designation for unified screw threads. This standard is currently controlled by ASME/ANSI in the United States. Several variations in thread form have been developed for unified threads in various other countries.

The standard was originally adopted by the Screw Thread Standardization Committees of Canada, the United Kingdom, and the United States on Nov 18, 1949 in Washington, D.C., and applied to screw threads used in the above countries with the hope they would be adopted universally. The original standard may be found in the ASA (now ANSI) publication, Vol. 1, 1949.

UTS may come as Unified Coarse (UNC[1] (http://homepages.tesco.net/~A10bsa/uncgo.htm)), Unified Fine (UNF [2] (http://homepages.tesco.net/~A10bsa/unfgo.htm)) or Unified Extra Fine 'UNEF.'

The International Organization for Standardization (ISO) preferred series, based on metric rounded numbers is the standard that has been adopted world-wide and has displaced all former standards, including UTS. In the USA, where UTS is still prevalent, over 40 % of products contains ISO preferred. Of the above mentioned countries, the UK has completely abandoned its commitment to UTS in favour of the ISO preferred series, and Canada is inbetween. As the remnant of products still using UTS complete the switch to ISO preferred, it is just a matter of time before the UTS vanishes completely.


Technical Information

Form and Pitch

UTS thread form and pitch technical specifications are currently controlled by ASME/ANSI industry standards in the United States:

  • ASME/ANSI B1.1 - 2003 Unified Inch Screw Threads, UN & UNR Thread Form
  • ASME/ANSI B1.10M - 2004 Unified Miniature Screw Threads
  • ASME/ANSI B1.15 - 1995 Unified Inch Screw Threads, UNJ Thread Form

Missing image

<math>P=1/Teeth Per Inch<math>
<math>H=0.866025 * P<math>
<math>H1=0.541266 * P<math>
<math>d2=d- 1.082532 * P<math>
<math>d1=d- 1.082532 * P<math>


A screw thread gaging system comprises a list of screw thread characteristics that must be inspected to establish the dimensional acceptability of the screw threads on a threaded product and the gage(s) which shall be used when inspecting those characteristics.

Curently this gaging UTS is controlled by:

  • ASME/ANSI B1.2-1983 Gages And Gaging For Unified Inch Screw Threads
  • ASME/ANSI B1.3M-1992 Screw Thread Gaging Systems Dimensional Acceptability Inch Metric Screw Threads

These Standards provide essential specifications and dimensions for the gages used on Unified inch screw threads (UN, UNR, UNJ thread form)on externally and internally threaded products. It also covers the specifications and dimensions for the thread gages and measuring equipment. The basic purpose and use of each gage are also described. It also establishes the criteria for screw thread acceptance when a gaging system is used.

Composer Kenneth Gaburo has used the text of the Unified Thread Standard as lyrics in his LINGUA II: MALEDETTO (Composition for 7 Virtuoso Speakers) 1967-8.

See also

Joseph Whitworth for another type of wire thread


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