Talk:Unified Thread Standard

Tap Drill Sizes
Added these in based on the sources in the external links, cross-checked against some other web sites: ,, and.

There's some discrepancies in the drill size for a 1-64 thread, source cite both #53 and #54. #53 is most common.

Pstemari (talk) 20:38, 1 September 2008 (UTC)

Is it normal for tap drill sizes to be in metric? — Preceding unsigned comment added by 121.220.134.226 (talk) 02:37, 19 March 2015 (UTC)


 * For metric threads, yes. For non-metric threads such as UTS threads (the subject of this article), no, it's not normal, but it is usually OK, as long as (1) the user understands and applies the concepts properly and (2) the requirements (per drawing, DPD, or informal need) allow it. The goal is a hole of a size that falls within a certain range, regardless of whose system of units is used to measure it. For example, for a 1/4-28 thread, both 5.5 mm and 5.6 mm drills make good tap drills for virtually any purposes, even though 7/32" is the principal tap drill. The idea is explained more at List of drill and tap sizes § Rules of thumb, and then worked examples are given at List of drill and tap sizes § Examples. The only thing that would stop someone from using a metric tap drill for a UTS thread is that by the book, if you are meeting a thread size callout to the letter, you technically should only use the tap drills named in the ASME/ANSI UTS standard tables. But in real life, on most products, if you use a 10 mm (.393") drill in place of either a 25/64" (.391") or a letter X (.397") when creating a 7/16-20 threaded hole, no one will ever have any reason to know, find out, or care. Physically, the differences between those 3 features (one made with each drill) are so small that to posit a context in which they are not negligible takes a lot of contrivance or rarity. By the way, the number drill series and letter drill series are imperial/customary series, not metric series (don't know whether this was realized). Cheers, — ¾-10 23:04, 19 March 2015 (UTC)

Switch
Unifed Thread Standard is not going away. It won't go away intill the US switches totaly over to metrics. Even after that it will be another 50 to 75 years untill UTS bolts and taps are stoped being produced. ISO and UTS are not interchangeable due to the smaller id on the minior dimater on the internal threads. This means that as long as there are machines in the world that are old we will still be using UTS. The 50 to 75 years for thoes machines to come totaly out of service.

- ctempleton3


 * In other words its a matter of time, but a long time? Hyacinth 18:11, 8 Mar 2005 (UTC)

Units?
I think the units in the table of preferred sizes are wrong. The column states that screw pitches are measured in units of 1/in? Can this be? I think the column should be labelled 'turns per inch' rather than 'pitch'. But perhaps I have misunderstood something. —Preceding unsigned comment added by 129.215.76.53 (talk) 12:19, 12 August 2008 (UTC)


 * "Pitch" is just the standard name of that physical quantity. A count of things (e.g., turns, threads) is a dimensionless quantity, i.e. a quantity that is stated using the unit 1. Dividing that by the unit of length used here (inch) leads to the correct overall unit 1/in or in−1, which you can pronounce as "per inch" (likewise mm−1 = "per millimeter", etc.). It all works out correctly in calculations: multiply a "12 in−1" pitch with a thread length of "3 in", the result will be "36", which has no unit because it is a count of turns. The fact that the units cancel each other out during multiplication suggests that the calculation didn't go wrong too badly, because we expected a dimensionless result. So looks all fine and correct.
 * Writing all quantities such that you can multiply out the units correctly, just like any other factor, is a common practice in the physical sciences and engineering worldwide. It helps in particular if you mix units: a screw with a "12 in−1" pitch that is 127 mm long will have 12 in−1 × 127 mm = (12×127) × (mm/in) = 1524 × (1/25.4) = 60 turns. Easy as π. Markus Kuhn (talk) 15:26, 16 August 2008 (UTC)

Colloquial name?
How do you call these threads colloquially? An ISO metric thread is called 'metric', but how do you call non-metric threads? -- Hokanomono ✉ 15:57, 2 May 2007 (UTC)


 * "Imperial," "English" or "inch." Or they are just referred to directly such as: "quarter-twenty" or “ten-thirty two.”--gargoyle888 19:46, 2 May 2007 (UTC)


 * I don't think that UNF or UNC can be 'Imperial'. In the UK Imperial standards are those defined in the Weights and Measures Act of 1824.  The Inch and Gallon are Imperial measurements, but no-one would call a Whitworth thread 'Imperial'.  Although BSP pipe threads, society microscope thread, and the standard brass thread were all defined in the Imperial era.  But for UNF/UNC I thought there had been some earlier war that had caused a rift across the atlantic - it is unlikely that an American Engineer would think his measures Imperial. I've only ever heard them called "Inch" threads, or (less than accurately) "standard".Brunnian (talk) 19:25, 5 August 2009 (UTC)

You have just said "The Inch and Gallon are Imperial measurements" So by that alone any thread of an inch measurement or fraction of has to be imperial. i.e. 3/4 unf or unc or bsw or whatever must be imperial likewise m10 by it's very size has to be and can only be metric. — Preceding unsigned comment added by 176.251.20.179 (talk) 14:23, 30 March 2015 (UTC)


 * In the United States these are often referred to as standard threads or SAE threads. Jayscore (talk) 18:03, 31 December 2009 (UTC)

The whole answer(s)
It is very true that there are various terms that are loosely used although not technically accurate, and there is an annoying lack of a compelling, simple, technically accurate blanket term that would enjoy widespread dominance in laypersons' usage. For example, "imperial" is often sloppily used as a blanket term, including in the U.S., even though from a technical perspective there are many important distinctions between true Imperial and American units of measure. "Customary units" is a term sometimes heard, but not on the shop floor as much as in writing. "English" is very often used generally, including in the U.S. on the shop floor, even though from a technical perspective there are important differences between American and British units. As Jayscore also mentions above, it is not uncommon to hear people (in the U.S. at least) use the term "SAE" to mean only "inch as opposed to metric", even though that usage is really unfortunate for how technically ignorant it is. But I believe that it is the reason why so many people mistakenly think that "SAE" stands for "Society of American Engineers" whereas it actually (used to) stand for "Society of Automotive Engineers" (it is no longer acronymous). People in the U.S. also often use the terms "U.S. standard (USS)", "American Standard", and just plain "standard" or "regular" to mean "inch-based as opposed to metric". Those are all unfortunate, sloppy usages. "USS" is way outdated (it was over half a century ago that the joint U.S.-U.K.-Commonwealth Unified Thread Standard superseded it). "American Standard" is outdated for similar reasons (and also happens to be an unfortunately chosen brand name for restroom fixtures). Using terms such as "standard", "regular", and "conventional" are always poor ways to handle retronymy, because they become increasingly ridiculous misnomers once the "new" way has been around for a really long time (hello metric system) and has halfway displaced the old way toward becoming the standard, conventional, or default way (hello U.S. use of metric). To summarize, the reason that there is no good, simple answer to this "colloquial name?" question is that the general public wallows in nomenclatural confusion and technical ignorance, and natural language reigns over controlled vocabulary. Probably the best colloquial blanket terms for nonmetric units in general that are both technically accurate and socially acceptable (i.e., even idiots will not balk upon hearing them) are "nonmetric" or "non-SI". And for the threads that this article is about, "inch-based thread standards" would work for laypeople, and "UNC" and "UNF" are probably the terms that shop-floor metalworkers would recognize most readily. But, as Gargoyle888 said above, usually the number itself is all they need to hear: "ten-thirty-two", "quarter-twenty", "half-twenty", "three-quarter-ten". — ¾-10 22:10, 31 December 2009 (UTC)

D versus D1 in diagram
I wonder why D and D1 in the diagram on this article are swapped compared to the otherwise (except for insignificant artistic details) identical diagram on the ISO metric screw thread article. I had thought, in both screw threads, the major diameter is the nominal diameter D, i.e. the one after which the thread is named. It would make more sense to me if D were the nominal diameter in both diagrams. Is this just a typo on Unified_Thread_Diagram.gif? I would have thought, the exact same diagram can be used to explain the Unified Thread Standard and ISO metric screw thread, and that both differ merely in their choices of major diameter and pitch values. Anyone here who has the UTS standard at hand to check? Markus Kuhn (talk) 20:36, 4 January 2008 (UTC)

Vectorizing diagram
Image improvement request: WP:GL/IMPROVE Markus Kuhn (talk) 20:41, 4 January 2008 (UTC)

UNS
My employer has started using UNS threads, which confused me enormously (I went metric in 1958). I have found some web pages that describe some: Where do they fit in? are they a real standard? Brunnian (talk) 11:34, 5 August 2009 (UTC)
 * http://www.efunda.com/DesignStandards/screws/unified.cfm
 * http://www.sizes.com/tools/thread_american.htm


 * I'm confused as to what your question is. It is a legit standard, and is the most common type of screw available in the United States. The two links you supplied have the dimensions for the various types available. Wizard191 (talk) 14:12, 5 August 2009 (UTC)


 * I've used many UNF and UNC screws, but only recently come across UNS. Is it really more common than UNF or UNC?  if so it should be on the main article page, and it isn't, which is why I was wondering if it was well-known. Brunnian (talk) 19:19, 5 August 2009 (UTC)


 * I think Wizard191 may have misspoke or he knows something that would surprise me. As part of writing and editing the Screw article I thought I became familiar with all the various designations for Unified thread standards, but I had forgotten about the UNS.  As per the second site you linked to it seems to stand for Unified National Special.  All of the sizes are "discouraged by standard organizations" category.
 * I'd be interested in knowing why your employer would use them. I doubt that you would find them for sale in any normal hardware stores or home centers.  It does seem that the article should have something to say about what the purpose of the UNS compliant fasteners is.  —Preceding unsigned comment added by Davefoc (talk • contribs) 19:56, 5 August 2009 (UTC)
 * The explanation I was given, which I thought at the time was hokum, was 'UNS is Unified Standard, a new standard intermediate between coarse and fine and intended to reduce the number of threads in use'. I made the query because a number of drawings showed threads as UNS, a series I was unfamiliar with. I recall thinking at the time that it was perverse to invent yet another non-metric thread rather than simply metricating, and I doubted any standards committee would do so. Not all of the explanations I am given at work are watertight. Brunnian (talk) 20:34, 8 August 2009 (UTC)
 * Sorry about that, DaveFoc is quite right, I misspoke; you wrote UNS but I read UTS and thought you were referring to the standard as a whole. Generally UNS threads are only used for "special" applications where one of the other threads won't work. One of the most common applications of a UNS thread that I have dealt with is with spindle threads. Wizard191 (talk) 21:18, 5 August 2009 (UTC)


 * I just reread what I wrote and I realize that I implied that I was a major contributor to the Screw article. I wrote and edited a small part of it and I didn't mean to imply otherwise. As to what Wizard191 wrote: I don't know what a spindle thread is. Are some UNS sizes readily available or are all or most of them made on request? I don't see what they might be used for except perhaps really annoying somebody that was trying to find a replacement for one of them.  Davefoc (talk) 01:32, 6 August 2009 (UTC)


 * Spindle threads = the thread on the end of your car spindle / axle, used to hold the rotating assembly on. Also, they are used on the spindles of some milling machines. They are almost never used for standard nut and bolt type applications, but instead where a fine thread is needed on a large OD and then have a specialized part with the mating thread; where I work we use a UNS thread in this way. On McMaster Carr you can buy UNS dies (http://www.mcmaster.com/#dies/=32ar6z see the fractional/machine screw drop down box) and taps (http://www.mcmaster.com/#taps/=32aubq). Wizard191 (talk) 02:43, 6 August 2009 (UTC)


 * What do you think about adding a small section on the UNS part of the unified standard to this article, Wizard191? It seems like what you've said here would be useful information. I'd like to hear from Brunnian again on this.  It seems doubtful that his employer could have switched to UNS for general purpose fasteners.  I doubt that they are available and it is hard to imagine a purpose for doing so.  I would expect, as Wizard191 suggests, that the use of UNS threads is limited to specialized applications.  The advantage of using UNS compliant threads where there is a need is that tooling and gauges are available so that when there is a special need one doesn't need to create the tooling from scratch for the threads.  Davefoc (talk) 18:05, 6 August 2009 (UTC)


 * I absolutely think that there should be a section about UNS threads in the article and have no problem writing it, but you'll have to bear with me as I've been very busy in real life and my time to edit articles has decreased. Wizard191 (talk) 18:15, 6 August 2009 (UTC)
 * >I'd like to hear from Brunnian again on this. - see reply above. Brunnian (talk) 20:34, 8 August 2009 (UTC)

1-14 UNF
My machinists and my fastener suppliers have told me that 1-12UNF is an old standard, and 1-14UNF is the new standard for 1" fine thread. I don't have access to the ANSI documents, so I can't reference those, however, these sites do reflect the change:, , Khawki02 (talk) 19:32, 15 December 2009 (UTC)


 * Quite right. I double checked it with my Machinery's handbook and fixed it on the page. Wizard191 (talk) 13:36, 16 December 2009 (UTC)

Inclusion of metric equivalent
The edit to include metric values included only one real value: "5.5"; the rest were just "mm". This is not a constructive edit. Seeing how this article is about customary units, I don't see the use in include metric equivalents, especially if there is only one. Instead, I added a note to the top of the table that references the Drill bit sizes article, for those interested in the exact metric conversion. Wizard191 (talk) 15:10, 30 August 2010 (UTC)
 * More interesting than exact conversions of the imperial sizes would be knowing which of the common metric drill sizes are appropriate for a given size of UNC tap. This would be useful information for those of us who live in metric countries but from time to time have to deal with stuff designed in america. 151.229.191.223 (talk) 15:31, 16 June 2014 (UTC)


 * That info ("which of the common metric drill sizes are appropriate for a given size of UNC tap") is indeed quite useful, as is the reverse here in the U.S. ("which of the common inch-based drill sizes are appropriate for a given size of metric tap"). I plan to eventually add them all to List of drill and tap sizes, but I don't know when I will get time to do it. This ties into a discussion at that talk page, Talk:List of drill and tap sizes > Errors in M6 and others. — ¾-10 02:31, 17 June 2014 (UTC)


 * Update: I added the rules of thumb to that article today (List of drill and tap sizes > Rules of thumb), which helps anyone looking for this info (by giving them the general case, from which they can figure out the instances). Someday when I have hours of free time to spend and not prioritized to another also-worthy activity, I will insert &lt;td&gt; into existing table rows, showing the specific instances for each size thread. — ¾-10 14:52, 19 June 2014 (UTC)

screw nut washer dimensions
This useful article is too limited. It lacks obvious links to comparable information about other aspects of screw dimensions (screw heads and tips), nuts, and washers. Please add good links to such information.-96.237.79.6 (talk) 11:59, 28 September 2010 (UTC)


 * See washer (hardware), nut (hardware), and list of screw drives. Wizard191 (talk) 17:52, 28 September 2010 (UTC)

ANC?
I booklet of thread sizes I was recently looked at listed a thread I measured/gauged as #6 ANC, the sizes also match the #6 UNC in this article.

Are UNC and ANC simply different names for the same thing? was there at some point a convention of calling the hash sizes ANC and the larger sizes UNC? (which is what this booklet appeared to be doing). Should any of this be mentioned in the article? Plugwash (talk) 08:55, 1 April 2011 (UTC)


 * From my research "ANC" is a very uncommon acronym for "American National Coarse" (with "ANF" relating to "American National Fine"). The common acronym for these are "NC" and "NF"; see . Wizard191 (talk) 20:48, 1 April 2011 (UTC)
 * Just so you know, this document states that the only difference between the two is the 1 inch TPI. Wizard191 (talk) 20:50, 1 April 2011 (UTC)


 * I think Wizard is right that ANC was probably being used to mean what's usually called NC (National Coarse). If a speaker is within the USA, then he knows which nation the "national" is implicitly referring to, but if he is anywhere else, he might call it American National Coarse to clarify the referent. That's my guess, worth 2 cents. — ¾-10 21:58, 1 April 2011 (UTC)


 * Note that i'm not in the US, i'm a brit who occasionally has to deal with american screws (we use metric on anything we design ourselves but we often have to deal with US imports). The booklet I was looking at was a list of threads sizes from various different standards.

IMO the "origins" section of the article should really have some actual content rather than just a link to a section of a more general article. In particular I would expect information on how unified national threads came about and their relationship to earlier threads. The United States Standard thread article linked from the screw thread article claims that national coarse and unified national coarse are compatible but with tolerance differences which is kind of contradicted by the FAA document Wizard191 linked (note: I fixed his link, it seems mediawiki doesn't like spaces in urls). I also notice that the United States Standard thread article says that the unified standard was introduced for larger sizes first. This may explain why the booklet reffers to some sizes as ANC and some as UNC Plugwash (talk) 17:05, 12 April 2011 (UTC)


 * I agree that the "origins" section should be expanded a bit. The Unified Thread Standard was derived from the United States Standard and the SAE standards and it only takes about one sentence to explain that much. References to more detailed discussions of the origin can still be included.


 * It also seems like the United States Standard Thread article has an error based on the document that wizard191 linked to. That article should be corrected on that point assuming that corroborating evidence can be found. --Davefoc (talk) 18:33, 12 April 2011 (UTC)
 * I looked in my Machinery's handbook to find the ref in the USS article, and my 25th edition doesn't have anything about the USS standard, so I'm a little dubious about that sentence. Wizard191 (talk) 19:17, 12 April 2011 (UTC)

Hi all. I think everything said here so far is sensible. I just have one caveat to add. The reason why "Origins" links out to another article is that the history of screw thread standardization makes more sense when covered in a unified place (no pun intended). If we covered only UTS history here, it would inevitably fork the historical coverage (of all of them—Whitworth, USS, BSA, UTS, pre-ISO metric, ISO), whereas I think it works better all in one place (because of the way that the standards influenced each other). Thanks for considering. — ¾-10 02:00, 13 April 2011 (UTC)

Dmaj in SVG Drawing
Isn't the Dmaj in the drawing actually the radius of the screw. Or in other words, should the drawing use Dmaj/2 for that dimension in the drawing? — Preceding unsigned comment added by Kentamanos (talk • contribs) 03:33, 31 August 2011 (UTC)


 * The drawing isn't wrong, it's just "jargony" in the sense that it's made for viewers who will take the intent as understood. The dot-dash line is a conventional way of representing the centerline of the cylinder, and each DIA's dimension line continues past it, rather than terminating in a second arrowhead right at centerline. If the latter were done, then "over two" (/2) would agree with it, but if doing "over two" then the dimension line would need to be changed. Even though it is correct as drawn, perhaps your suggested way is better for a general-audience encyclopedia. If anyone gets time to modify, that would be fine. — ¾-10 23:52, 2 September 2011 (UTC)

Important mistake
the table of screw sizes says major diamter but writes the minor diamters. — Preceding unsigned comment added by 188.120.137.254 (talk) 17:33, 12 January 2013 (UTC)


 * Nope, the table is correct—the left-hand column lists major (not minor) diameter, and the columns on the right list the tap drill sizes. — ¾-10 19:58, 12 January 2013 (UTC)

UNO thread?
Is there a UNO thread? Lamps and lamp shades identified as "UNO" or "Uno" are commonplace. Does "UNO" refer to the fine thread on the outside of the bulb socket near the glass? PeterEasthope (talk) 23:47, 6 January 2014 (UTC)
 * Most traditional bulb thread sizes are "ES" (Edison Screw) and the diameter in millimetres. See https://en.wikipedia.org/wiki/Edison_screw  Darkman101 (talk) 02:48, 9 December 2015 (UTC)
 * UNO thread on a lamp socket or lamp shade refers to the thread on the outside shell of a lamp socket and the inside thread of the shade fitter of the lamp shade. UNO sockets allow threading a lmmp shade directly on to the lamp socket. — Preceding unsigned comment added by Joe-tuttle (talk • contribs) 18:01, 2 January 2017 (UTC)

Gauge numbers
Hi, the article should mention the gauge system referred to by the numbers #0 .. #12. I don't have a copy of ASME/ANSI B1.1 at hand. It would cite the gauge, which would have existed before the thread standard. Regards, ... PeterEasthope (talk) 19:11, 5 August 2020 (UTC)

Does a fully commercial website belong on a Wikipedia page? Suggestion
With regards to the section Notes: item #3: This is a link to a COMMERCIAL website. Wikipedia pages that include information about specific materials does not grant an automatic license to add 'related' commercial links, as most people do know. But apparently not the person who edited this page by adding the link, I guess? While perhaps the occasional viewer may find this link useful, I do believe it really is completely inappropriate here. I just happened to stumble on it, and thought I'd point it out. Not to put too fine a point on it, but commercial links embedded within Wikipedia pages runs counter to the accessible and unbiased ethos around which Wikipedia was created and exists today. The appropriate place for any online commercial endeavour is of course the WWW, through the use of search engines. Certainly not by looking for items offered for sale via Wikipedia pages. Thanks for considering the removal of this commercial link.

Origin of # Formula
Does anyone know the origin of the formula: Major diameter = Screw # × 0.013 in + 0.060 in. How were the values of 0.013" and 0.060" determined? The only information I was able to find online regarding this is this forum where the question is posed and not answered and this site which claims that strength of the screw is doubled as the # increases, however, when calculating strength based on tensile stress area this claim is incorrect; the ratio ranges from 1.1 to 1.5. Thanks in advance. Acolosi22 (talk) 19:03, 7 March 2023 (UTC)