Editing Unified Thread Standard (section)

==Designation==

The standard designation for a UTS thread is a number indicating the nominal (major) diameter of the thread, followed by the pitch measured in [[threads per inch]]. For diameters smaller than {{sfrac|1|4}} inch, the diameter is indicated by an integer number defined in the standard; for all other diameters, the inch figure is given.

This number pair is optionally followed by the letters UNC, UNF or UNEF (Unified) if the diameter-pitch combination is from the ''coarse'', ''fine'', or ''extra fine'' series, and may also be followed by a tolerance class.

Example: #6-32 UNC 2B (major diameter: 0.1380&nbsp;inch, pitch: 32 tpi)

{| class="wikitable"
|+ Unified Screw Threads — UNC, UNF and UNEF{{sfnp|''Machinery's Handbook'' 29|2012|p=[https://archive.org/details/machineryshandbo0000unse_f4b1_29edition/page/1816/ 1816]}}
|-
! colspan=3 rowspan=3 | Major diameter<br />''D''<sub>maj</sub> (inch, mm)
! colspan=9 | Thread density (''d'', [[Screw thread#Lead, pitch, and starts|threads per inch]]) and thread [[lead (engineering)|pitch]] (''p'')
! colspan=6 rowspan=2 | [[Drill bit sizes#Drill Bit Conversion Table|Preferred]] cutting [[list of drill and tap sizes|tap drill size]]
|-
! colspan=3 | Coarse (UNC)
! colspan=3 | Fine (UNF)
! colspan=3 | Extra fine (UNEF)
|-
! ''d'' ([[threads per inch|TPI]])
! colspan=2 | ''[[Pitch (screw)|p]]'' (inch, mm)
! ''d'' (TPI)
! colspan=2 | ''p'' (inch, mm)
! ''d'' (TPI)
! colspan=2 | ''p'' (inch, mm)
! colspan=2 | Coarse
! colspan=2 | Fine
! colspan=2 | Extra fine
|-
| #0 || {{convert|0.0600|in|mm|4|abbr=values|disp=table}} ||colspan=3 {{n/a|None}} || 80 || {{convert|0.012500|in|mm|4|abbr=values|disp=table}} ||colspan=3 {{n/a|None}} ||colspan=2| || {{sfrac|3|64}}″ || .047 ||colspan=2| 
|-
| #1 || {{convert|0.0730|in|mm|4|abbr=values|disp=table}} || 64 || {{convert|0.015625|in|mm|abbr=values|disp=table}} || 72 || {{convert|0.013888|in|mm|abbr=values|disp=table}} ||colspan=3 {{n/a|None}} || #53 || .060 || #53 || .060 ||colspan=2| 
|-
| #2 || {{convert|0.0860|in|mm|4|abbr=values|disp=table}} || 56 || {{convert|0.017857|in|mm|abbr=values|disp=table}} || 64 || {{convert|0.015625|in|mm|abbr=values|disp=table}} ||colspan=3 {{n/a|None}} || #50 || .070 || #50 || .070 ||colspan=2| 
|-
| #3 || {{convert|0.0990|in|mm|4|abbr=values|disp=table}} || 48 || {{convert|0.020833|in|mm|abbr=values|disp=table}} || 56 || {{convert|0.017857|in|mm|abbr=values|disp=table}} ||colspan=3 {{n/a|None}} || #47 || .079 || #45 || .082 ||colspan=2| 
|-
| #4 || {{convert|0.1120|in|mm|4|abbr=values|disp=table}} || 40 || {{Convert|0.025000|in|mm|4|abbr=values|disp=table}} || 48 || {{convert|0.020833|in|mm|abbr=values|disp=table}} ||colspan=3 {{n/a|None}} || #43 || .089 || #42 || .094 ||colspan=2| 
|-
| #5 || {{convert|0.1250|in|mm|4|abbr=values|disp=table}} || 40 || {{Convert|0.025000|in|mm|4|abbr=values|disp=table}} || 44 || {{convert|0.022727|in|mm|abbr=values|disp=table}} ||colspan=3 {{n/a|None}} || #38 || .102 || #37 || .104 ||colspan=2| 
|-
| #6 || {{convert|0.1380|in|mm|4|abbr=values|disp=table}} || 32 || {{convert|0.031250|in|mm|abbr=values|disp=table}} || 40 || {{Convert|0.025000|in|mm|4|abbr=values|disp=table}} ||colspan=3 {{n/a|None}} || #36 || .107 || #33 || .113 ||colspan=2| 
|-
| #8 || {{convert|0.1640|in|mm|4|abbr=values|disp=table}} || 32 || {{convert|0.031250|in|mm|abbr=values|disp=table}} || 36 || {{convert|0.027778|in|mm|abbr=values|disp=table}} ||colspan=3 {{n/a|None}} || #29 || .136 || #29 || .136 ||colspan=2| 
|-
| #10 || {{convert|0.1900|in|mm|4|abbr=values|disp=table}} || 24 || {{convert|0.041667|in|mm|abbr=values|disp=table}} || 32 || {{convert|0.031250|in|mm|abbr=values|disp=table}} ||colspan=3 {{n/a|None}} || #25 || .150 || #21 || .159 ||colspan=2| 
|-
| #12 || {{convert|0.2160|in|mm|4|abbr=values|disp=table}} || 24 || {{convert|0.041667|in|mm|abbr=values|disp=table}} || 28 || {{convert|0.035714|in|mm|abbr=values|disp=table}} || 32 || {{convert|0.031250|in|mm|abbr=values|disp=table}} || #16 || .177 || #14 || .182 || {{sfrac|3|16}}″ || .188
|-
| {{sfrac|1|4}}″ || {{convert|0.2500|in|mm|4|abbr=values|disp=table}} || 20 || {{convert|0.050000|in|mm|4|abbr=values|disp=table}} || 28 || {{convert|0.035714|in|mm|abbr=values|disp=table}} || 32 || {{convert|0.031250|in|mm|abbr=values|disp=table}} || #7 || .201 || #3 || .213 || {{sfrac|7|32}}″ || .219
|-
| {{sfrac|5|16}}″|| {{convert|0.3125|in|mm|4|abbr=values|disp=table}}|| 18 || {{convert|0.055556|in|mm|abbr=values|disp=table}} || 24 || {{convert|0.041667|in|mm|abbr=values|disp=table}} || 32 || {{convert|0.031250|in|mm|abbr=values|disp=table}} || F || .257 || I || .272 || {{sfrac|9|32}}″ || .281
|-
| {{sfrac|3|8}}″ || {{convert|0.3750|in|mm|4|abbr=values|disp=table}} || 16 || {{convert|0.062500|in|mm|abbr=values|disp=table}} || 24 || {{convert|0.041667|in|mm|abbr=values|disp=table}} || 32 || {{convert|0.031250|in|mm|abbr=values|disp=table}} || {{sfrac|5|16}}″ || .313 || Q || .332 || {{sfrac|11|32}}″ || .344
|-
| {{sfrac|7|16}}″|| {{convert|0.4375|in|mm|4|abbr=values|disp=table}}|| 14 || {{convert|0.071428|in|mm|abbr=values|disp=table}} || 20 || {{convert|0.050000|in|mm|4|abbr=values|disp=table}} || 28 || {{convert|0.035714|in|mm|abbr=values|disp=table}} || U || .368 || {{sfrac|25|64}}″ || .391 || Y || .404
|-
| {{sfrac|1|2}}″ || {{convert|0.5000|in|mm|4|abbr=values|disp=table}} || 13 || {{convert|0.076923|in|mm|abbr=values|disp=table}} || 20 || {{convert|0.050000|in|mm|4|abbr=values|disp=table}} || 28 || {{convert|0.035714|in|mm|abbr=values|disp=table}} || {{sfrac|27|64}}″ || .422 || {{sfrac|29|64}}″ || .453 || {{sfrac|15|32}}″ || .469
|-
| {{sfrac|9|16}}″|| {{convert|0.5625|in|mm|4|abbr=values|disp=table}}|| 12 || {{convert|0.083333|in|mm|abbr=values|disp=table}} || 18 || {{convert|0.055556|in|mm|abbr=values|disp=table}} || 24 || {{convert|0.041667|in|mm|abbr=values|disp=table}} || {{sfrac|31|64}}″ || .484 || {{sfrac|1|2}}″ || .500 || {{sfrac||33|64}}″ || .516
|-
| {{sfrac|5|8}}″ || {{convert|0.6250|in|mm|4|abbr=values|disp=table}} || 11 || {{convert|0.090909|in|mm|abbr=values|disp=table}} || 18 || {{convert|0.055556|in|mm|abbr=values|disp=table}} || 24 || {{convert|0.041667|in|mm|abbr=values|disp=table}} || {{sfrac||17|32}}″ || .531 || {{sfrac||9|16}}″ || .563 || {{sfrac||37|64}}″ || .578
|-
| {{sfrac|3|4}}″ || {{convert|0.7500|in|mm|4|abbr=values|disp=table}} || 10 || {{convert|0.100000|in|mm|abbr=values|disp=table}} || 16 || {{convert|0.062500|in|mm|abbr=values|disp=table}} || 20 || {{convert|0.050000|in|mm|4|abbr=values|disp=table}} || {{sfrac|21|32}}″ || .656 || {{sfrac|11|16}}″ || .688 || {{sfrac||45|64}}″ || .703
|-
| {{sfrac|7|8}}″ || {{convert|0.8750|in|mm|4|abbr=values|disp=table}} || 9 || {{convert|0.111111|in|mm|abbr=values|disp=table}} || 14 || {{convert|0.071428|in|mm|abbr=values|disp=table}} || 20 || {{convert|0.050000|in|mm|4|abbr=values|disp=table}} || {{sfrac||49|64}}″ || .766 || {{sfrac||51|64}}″ || .797 || {{sfrac||53|64}}″ || .828
|-
| 1″ || {{convert|1.0000|in|mm|4|abbr=values|disp=table}}
| 8 || {{convert|0.125000|in|mm|abbr=values|disp=table}}
| 12{{efn|For many years non-standard 1-inch 14-tpi nuts and bolts have been widely used instead of standard-sized 1-inch 12-tpi fasteners; consequently 1″-14 fasteners are easier to find and less expensive than 1″-12 fasteners. After several decades 1″-14 fasteners have now come to be commonly referred to as "Standard Fine Thread" or "UNF". Though technically incorrect (the UNF standard specifies 1″-12), size 1″-14 is universally accepted as standard for fine-threaded 1-inch fasteners, and "1-inch 14-tpi NF" has become established as a "common use" term, or "a genericized brand name/standard". In other words, the 1″-12 standard has lacked effective enforcement for a long enough time (many decades) to give [[generic trademark]]–like status to 1-inch 14-tpi fasteners.}}
| {{convert|0.083333|in|mm|abbr=values|disp=table}}
| 20 || {{convert|0.050000|in|mm|abbr=values|disp=table}}
| {{sfrac|7|8}}″ || .875 || {{sfrac|59|64}}″ || .922 || {{sfrac|61|64}}″ || .953
|-
| {{sfrac|1|1|8}}″ || 1.1250 || style="text-align:right;" | 28.5750
|  7 || 0.142857 || 3.6286
| 12 || {{convert|0.083333|in|mm|abbr=values|disp=table}} 
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
| {{sfrac|1|1|4}}″ || 1.2500 || style="text-align:right;" | 31.7500
|  7 || 0.142857 || 3.6286
| 12 || {{convert|0.083333|in|mm|abbr=values|disp=table}} 
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
| {{sfrac|1|3|8}}″ || 1.3750 || style="text-align:right;" | 34.9250
|  6 || 0.166667 || 4.2333
| 12 || {{convert|0.083333|in|mm|abbr=values|disp=table}} 
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
| {{sfrac|1|1|2}}″ || 1.5000 || style="text-align:right;" | 38.1000
|  6 || 0.166667 || 4.2333
| 12 || {{convert|0.083333|in|mm|abbr=values|disp=table}} 
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
| {{sfrac|1|3|4}}″ || 1.7500 || style="text-align:right;" | 44.4500
| 5 || 0.200000 || 5.0800
| colspan=3 |
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
| 2″ || 2.0000 || style="text-align:right;" | 50.8000
| {{sfrac|4|1|2}} || 0.222222 || 5.6444
| colspan=3 |
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
| {{sfrac|2|1|4}}″ || 2.2500 || style="text-align:right;" | 57.1500
| {{sfrac|4|1|2}} || 0.222222 || 5.6444
| colspan=3 |
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
| {{sfrac|2|1|2}}″ || 2.5000 || style="text-align:right;" | 63.5000
| 4 || 0.250000 || 6.3500
| colspan=3 |
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
| {{sfrac|2|3|4}}″ || 2.7500 || style="text-align:right;" | 69.8500
| 4 || 0.250000 || 6.3500
| colspan=3 |
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
|3″ || 3.0000 || style="text-align:right;" | 76.2000
| 4 || 0.250000 || 6.3500
| colspan=3 |
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
| {{sfrac|3|1|4}}″ || 3.2500 || style="text-align:right;" | 82.5500
| 4 || 0.250000 || 6.3500
| colspan=3 |
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
| {{sfrac|3|1|2}}″ || 3.5000 || style="text-align:right;" | 88.9000
| 4 || 0.250000 || 6.3500
| colspan=3 |
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
| {{sfrac|3|3|4}}″ || 3.7500 || style="text-align:right;" | 95.2500
| 4 || 0.250000 || 6.3500
| colspan=3 |
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|-
| 4″ || 4.0000 || style="text-align:right;" | 101.6000
| 4 || 0.250000 || 6.3500
| colspan=3 |
| colspan=3 |
| colspan=2 |
| colspan=2 |
| colspan=2 |
|}
{{noteslist}}

The following formula is used to calculate the major diameter of a numbered screw greater than or equal to 0: ''Major diameter'' = ''Screw #'' × 0.013&nbsp;in + 0.060&nbsp;in. For example, the major diameter of a #10 screw is 10 × 0.013&nbsp;in + 0.060&nbsp;in = 0.190&nbsp;in. To calculate the major diameter of "aught" size screws count the number of extra zeroes and multiply this number by 0.013&nbsp;in and subtract from 0.060&nbsp;in. For example, the major diameter of a #0000 screw is 0.060&nbsp;in − (3 × 0.013&nbsp;in) = 0.060&nbsp;in − 0.039&nbsp;in = 0.021&nbsp;in.

The number series of machine screws has been extended downward to include #00-90 (0.047&nbsp;in = 0.060&nbsp;in − 0.013&nbsp;in) and #000-120 (0.034&nbsp;in = 0.060&nbsp;in − 2 × 0.013&nbsp;in) screws;<ref>[http://www.metricscrews.us/index.php?main_page=index&cPath=79 #00-90 and #000-120 screws for sale]</ref> however, the main standard for screws smaller than #0 is ANSI/ASME standard B1.10 Unified Miniature Screw Threads. This defines a series of metric screws named after their major diameters in millimetres, from 0.30&nbsp;UNM to 1.40&nbsp;UNM. Preferred sizes are 0.3, 0.4, 0.5, 0.6, 0.8, 1.0 and 1.2&nbsp;mm, with additional defined sizes halfway between.{{sfnp|''Machinery's Handbook'' 29|2012|p=[https://archive.org/details/machineryshandbo0000unse_f4b1_29edition/page/1861/ 1861]}}  The standard thread pitch is approximately {{sfrac|1|4}} of the major diameter. The thread form is slightly modified to increase the minor diameter, and thus the strength of screws and taps. The major diameter still extends to within {{sfrac|1|8}}''H'' of the theoretical sharp ''V'', but the total depth of the thread is reduced 4% from {{sfrac|5|8}}''H'' = {{sfrac|5|8}}&nbsp;cos(30°)&nbsp;''P'' ≈ 0.541''P'' to 0.52''P''.{{sfnp|''Machinery's Handbook'' 29|2012|pp=[https://archive.org/details/machineryshandbo0000unse_f4b1_29edition/page/1858/ 1858–1859]}} This increases the amount of the theoretical sharp ''V'' which is cut off at the minor diameter by 10% from 0.25''H'' to {{sfrac|7|8}} − {{sfrac|0.52|cos 30°}} ≈ 0.27456''H''.

The number series of machine screws once included more [[odd number]]s and went up to #16 or more. Standardization efforts in the late 19th and the early part of the 20th century reduced the range of sizes considerably. Now, it is less common to see machine screws larger than #14, or odd number sizes other than #1, #3 and #5. Even though #14 and #16 screws are still available, they are not as common as sizes #0 through #12.{{Citation needed|date=December 2009}}

Sometimes "special" diameter and pitch combinations (UNS) are used, for example a {{convert|0.619|in|abbr=on}} major diameter with 20 threads per inch. UNS threads are rarely used for bolts, but rather on nuts, tapped holes, and threaded ODs. Because of this UNS taps are readily available.<ref>{{cite web |author= McMaster-Carr |title= Special Thread Size Round Adjustable Threading Dies |page=2520 |url= http://www.mcmaster.com/#catalog/115/2520/=3dxzrr |access-date= 2024-12-24}}</ref><ref>{{cite web |author= McMaster-Carr |title= Special Thread Size High-Speed Steel Hand Taps |page= 2501 |url= http://www.mcmaster.com/#catalog/115/2501/=3dy2xw |access-date=2024-12-24}}</ref> Most UNS threads have more threads per inch than the correlating UNF or UNEF standard; therefore they are often the strongest thread available.{{sfnp|Schwaller|2004|p=55}} Because of this they are often used in applications where high [[Stress (mechanics)|stresses]] are encountered, such as [[Spindle (tool)|machine tool spindles]]<ref>{{cite web |title= Special connections |website= Filton Rotary Union Products |url= http://www.nuraseal.com/Filton/Special_Connections/Special_Connections.htm |access-date=2009-08-28 |archive-date=18 May 2009 |archive-url=https://web.archive.org/web/20090518141122/http://www.nuraseal.com/Filton/Special_Connections/Special_Connections.htm |url-status=dead }}.</ref> or [[Spindle (automobile)|automotive spindles]].<ref>{{cite web |title= Hub components |url= http://i.b5z.net/i/u/1080235/f/parts_kit_cat_8-08/Hub_Components.pdf |access-date=2009-08-29 |archive-date=17 June 2009 |archive-url= https://web.archive.org/web/20090617032130/http://i.b5z.net/i/u/1080235/f/parts_kit_cat_8-08/Hub_Components.pdf |url-status=dead }}.</ref>