Talk:British Association screw threads

Odd Sizes Rare

This counts as original research, but it should be noted in this article that odd sizes of BA fasteners are rare, most electrical and electronic equipment at least uses even numbered sizes. If I can find a citation for this I'll add it. Old Aylesburian (talk) 09:31, 2 May 2008 (UTC)

True. A few of the publications listed in the ref section of Preferred number may be apt (if anyone has time to correlate them to this article). — ¾-10 14:22, 2 May 2008 (UTC)

But they are still readily available in the UK, as are fasteners with 'one size smaller' heads down to 8BA i.e. 8BA threads made from 9BA stock. 78.33.116.240 (talk) 12:58, 12 April 2010 (UTC)

To be exact, the situation was that electrical/electronic assemblies generally used the even numbered sizes and purely mechanical assemblies used the odd sizes. However, the mechanics abandoned BA screw sizes before their electrical counterparts did giving the impression that only the even sizes were in general use. 86.144.90.137 (talk) 16:49, 13 September 2012 (UTC)

BS 93:2008 does recommend (p. 4) that even-numbered sizes be preferred. bjh21 (talk) 21:29, 6 October 2012 (UTC)

I understand the exact pitch of BA threads to be based on an integer of threads per centimeter, ie 0BA is 10 tpc, 1BA is 11tpc, etc. —Preceding unsigned comment added by Paull69 (talk • contribs) 03:15, 26 May 2008 (UTC)

False. The 0.9 relationship and coincidence means taht many threads approximate an exact number. 78.33.116.240 (talk) 12:58, 12 April 2010 (UTC)

Using the rule that pitch in mm = 1.0*0.9^(BA number) and taking 1 inch to be 25.4mm, I get the table below:

 BA      Pitch (mm)    Pitch (in)    Threads/mm    Threads/in       TPI from Article
  0        1.0000        0.0394        1.0000       25.4000           25.38  low
  1        0.9000        0.0354        1.1111       28.2222           28.25  high
  2        0.8100        0.0319        1.2346       31.3580           31.35  low
  3        0.7290        0.0287        1.3717       34.8422           34.84  even
  4        0.6561        0.0258        1.5242       38.7136           38.46  low
  5        0.5905        0.0232        1.6935       43.0151           43.10  high
  6        0.5314        0.0209        1.8817       47.7946           47.85  high
  7        0.4783        0.0188        2.0908       53.1051           52.91  low
  8        0.4305        0.0169        2.3231       59.0057           59.17  high
  9        0.3874        0.0153        2.5812       65.5618           64.94  low
 10        0.3487        0.0137        2.8680       72.8465           72.46  low

The TPI numbers don't correspond to those in the article (given in the rightmost column) and there doesn't appear to be any kind of pattern. In some cases the figures given in the article are less than the calculated values and in other cases they are high.

The 25.38 TPI given in the article for 0BA TPI strikes me as plain wrong. If the pitch is exactly 1.0 mm and 1 inch is exactly 25.4mm there have to be exactly 25.4 threads per inch. The only possibility I can think of that might explain the figure given is that at the time the BA system was created the inch had yet to be defined as being exactly 25.4mm. Possibly the table gives threads per old inch, but was the old inch really all that different, and if this was the issue wouldn't all of the TPI figures be low?

I actually suspect that the TPI figures given are probably correct (aside from the first one) as I've seen 59.17 TPI for 8 BA (to give one example) in a lot of other places, and that the rule for pitch involves some kind of rounding and/or truncation that is not explained in the article. Perhaps, for example, the pitch in mm has to be rounded to some number of decimal places. I've experimented with several rounding and truncation schemes but have so far been unable to come up with one that produces the figures given.

If anybody can shed light it would be appreciated. 70.26.15.69 (talk) 13:07, 23 February 2014 (UTC)

I'm afraid that I've really no idea how this talk feature works but I can be reached at bryant@sce.carleton.ca.

Further to the above, I think that I've found my answer (and that the table in the article is definitely incorrect).

In the "Model Engineer's Handbook" by "Tubal Cain" (T. D. Walshaw) it is stated that "the pitch of each BA thread is 0.9 times the pitch of the next larger size, rounded off to the nearest 0.01mm". I have tried using this rule and have found that it is consistent with the tabulated data in the same book provided that when a value can be rounded either way it is always be rounded to an odd number of 0.01 mm. This affects 11BA (0.315 mm is rounded down to is 0.31 mm) and 14BA (0.225 mm is rounded up to 0.23 mm).

The table becomes:

BA      Pitch (mm)    Pitch (in)    Threads/mm    Threads/in      Handbook TPI
  0        1.0000        0.0394        1.0000       25.4000           25.4
  1        0.9000        0.0354        1.1111       28.2222           28.2
  2        0.8100        0.0319        1.2346       31.3580           31.4
  3        0.7300        0.0287        1.3699       34.7945           34.8
  4        0.6600        0.0260        1.5152       38.4848           38.5
  5        0.5900        0.0232        1.6949       43.0508           43.1
  6        0.5300        0.0209        1.8868       47.9245           47.9
  7        0.4800        0.0189        2.0833       52.9167           52.9
  8        0.4300        0.0169        2.3256       59.0698           59.1
  9        0.3900        0.0154        2.5641       65.1282           65.1
 10        0.3500        0.0138        2.8571       72.5714           72.6
 11        0.3100        0.0122        3.2258       81.9355           81.9
 12        0.2800        0.0110        3.5714       90.7143           90.7
 14        0.2300        0.0091        4.3478      110.4348           110
 16        0.1900        0.0075        5.2632      133.6842           134
 18        0.1500        0.0059        6.6667      169.3333           169

The TPI values in the handbook are described as approximate and are only given to three figures. In every case the approximate value matches the result of rounding the calculated result to three figures. The handbook does give exact pitch values and these match those calculated.

The rounding means that 100 threads always take up an integral number of mm (possibly the source of the earlier suggestion regarding the number of threads in a cm?). This has practical implications in terms of cutting threads on a lathe. If there were no rounding (i.e. if each pitch was exactly 0.9 of the next larger pitch), being able to cut all possible BA threads would require either impossibly large change gears or an impractically large number of gear chain stages. Rounding changes the picture completely and makes it practical to cut all BA threads using a relatively modest number of reasonably sized change gears. 70.26.15.69 (talk) 19:57, 23 February 2014 (UTC)

History

It wouold be useful to add some information about when the BA standard was introduced. ie from when would BA threads become common and before when would BA threads not have existed.

Done.

The thread used in preference for 0BA for 6BA was 1/4" Whitworth, not 7/32", according to my copy of Machinery's Handbook. The Yowser (talk) 13:01, 12 April 2010 (UTC)

Very small sizes

Could anyone clarify or provide a source for the sentence "The very small sizes are not used very often and other standards tend to be used (e.g., NHS)"? What is an NHS thread? I cannot find a reference to it in Wikipedia, Google or any reference book I have. (Surely not 'National Hose Standard' - they are not miniature threads). What other standards are or were there for 'very small sizes?' Stephen2810 (talk) 12:54, 6 May 2013 (UTC)

A bit of googling seems to suggest that the "NHS" referred to is the Swiss standard used for watches, "Norme Horologe Suisse". But I have failed to find any details of the dimensions. 136.8.33.68 (talk) 12:03, 1 October 2018 (UTC)

and surely not our beloved National Health Service? then again...NHS MartUK2012 (talk) 03:00, 20 May 2015 (UTC) I think it refers to a small thread standard that is actually called NIHS. It is a standard that was used by the Swiss Horological Association for making clocks and watches. [TM]. — Preceding unsigned comment added by 2A02:C7F:8A24:B200:712E:699A:10F3:BA41 (talk) 14:04, 20 August 2017 (UTC)

Could somebody please clarify the beginning of the rather large run-on sentence, "Generally, the 0BA size was dropped in place of 7/32" BSF in assemblies that included larger fasteners, however, in smaller equipment that was primarily electronic/electrical the 0BA size would typically be used in place of the BSF or BSW screw where it was the largest size required." ? How can something be both dropped AND in place of? As an old UK radio amateur I do still have a modest collection of BA size nuts and bolts. I arrived here while looking for a BA thread gauge with which to identify them in amongst a somewhat larger collection of metric sized ones. As a youngster I could do it by feel, later by sight, but now I need some help.

73's G8EAD MartUK2012 (talk) 03:12, 20 May 2015 (UTC)

Re "dropped AND in place of"—I think the writer meant "dropped in favor of" ... "used in place of". (But I can't answer whether they were correct about it.) — ¾-10 22:35, 22 May 2015 (UTC)

Fixed. Globbet (talk) 17:14, 27 April 2021 (UTC)

BA Spanner Sizes

If anyone has the information, please would they add the spanner size for each BA thread ? Many thanks ! Darkman101 (talk) 00:58, 10 August 2015 (UTC)

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Formulae

"The pitch of 0BA is 1 mm and the pitch of each higher numbered thread is obtained by multiplying the pitch of the lower number by 0.9 so K-BA has a pitch of p = 0.9K rounded to two significant figures in mm. The major diameter is given by 6p1.2, rounded to two significant figures in mm and the hex head size (across the flats) is 1.75 times the major diameter." In this paragraph in the current article there are some superscripted "12"s after the references. What do they mean? Thanks 213.31.166.49 (talk) 12:57, 25 February 2023 (UTC)