Whit Form threads

[Howard Lewis]

On Howard Lewis Said:

Whitworth form threads are used in BSW, BSF, BSP, BSB (British Standard Brass) and Model Engineer threads, All of which have their own pitch or pitches. The only ” constant pitch” across all sizes are the BSB at 26 tpi, and the ME threads at 40 tpi and 32 tpi.

There will be other “non standard” pitches, (The early Myford ML1,2,3 and 4, used 7/8 BSW, and then 7/8 x 12 tpi, the “Standard” Myford 1.125 x 12 tpi.  The Warco BH600, BH900, Chester Craftsman, Engineers ToolRoom BL12 -24 all use 2.25 x 8 tpi for the chuck mounting, as no doubt, will other Taiwanese generic lathes.

Posibly Boxford will use a Whit form thread, to distinguish from the South Bend.

Sometimes a “non standard” pitch will be used, deliberately, sometimes to try to maintain a market for spare parts, or finer pitch than the standard for a given diameter, to provode a more precise adjustment.

R P S threads, used in older cameras, lenses and enlargers will be Whit form, but with a finer than standard pitch, plus microscopes.

Howard

Expanding on the mention of RPS threads: The “Leica thread” originally used for the thread mount for the Leica camera, is 39 mm diameter, 26 threads per inch, Whitworth form. Leica replaced this in 1954 with their M- series camera which used a bayonet mount. The 39 mm -26 TPI thread continued to be commonly used on enlarger lenses. It’s said that since E. Leitz already made microscopes, including objectives with the RMS thread, that lead to using an inch pitch – Whitworth form thread for their 35 mm camera lens mount.

I’ve come across statements to the effect that  tripod mounting screw threads were Whitworth form. Today they are 1/4 and 3/8 UNC, see ISO 1222.

I find the subject of screw threads to be fascinating.

 

David

[Nigel Graham 2Participant @nigelgraham2]

BA is metric although specified in inches, and based on an old Swiss thread (Thury?); but it makes more sense when you consider it proceeds as a geometrical progression, broken by the BSI committee who recommended the odd sizes not necessary! Still an overly-complicated system though.

Our Ornamental Turning brethren have to contend with yet another series again when restoring or repairing Holtzappfel lathes. The London-based manufacturer devised its own thread for at least certain parts on their products. [Incidentally, they are in Royal company: ornamental-turning was one of King George III’s hobbies.]

‘

At least the inch sizes, both British or American, use fairly regular rules for diameter increments and head proportions. The UNF hexagons are particularly neat and tidy. ISO-M Coarse (the “ordinary” ones) and Fine don’t seem to follow anything very regular at all in both diameters and spanner sizes, and whilst I can recall the common ones when looking for the spanner, I do wonder how they developed.

Could that result from many metric countries trying to agree on common dimensions in the mystery committees that are the ISO? (Larded with heavy lobbying? Surely not!)

 

That’s even before car and architectural-fastenings makers go and give ISO-standard threads, non-standard hexagons. My club’s portable track is assembled with M10 studs holding commercially-available flanged nuts from the builders’ merchants; and for no conceivable reason those take some odd spanner size you hope will fit the exaggerated, crudely-forged draught-angles.

[Mark RandParticipant @markrand96270]

BA is specified entirely in metric 🙂 6mm diameter and 1mm thread pitch for 0BA. Every subsequent size is 0.9 times the diameter and pitch of the previous one.

Rounded to the nearest thou for mere mortals, though.

[Mark Rand]

On Mark Rand Said:

BA is specified entirely in metric 🙂 6mm diameter and 1mm thread pitch for 0BA. Every subsequent size is 0.9 times the diameter and pitch of the previous one.

Rounded to the nearest thou for mere mortals, though.

Although based upon 0BA is based upon 6mm dia and 1mm pitch, isn’t the thread actually specified in fractions of an inch in the standard? It and the one it was copied from are perhaps, however, the only thread series based upon a mathematical and scientifically logical series?

[Nigel Graham 2]

On Nigel Graham 2 Said:

The UNF hexagons are particularly neat and tidy.

Is there a useful guide somewhere showing how to distinguish a UNF hexagon from a UNC hexagon?

Will the world end if I find a UNF hexagon on a UNC threaded item?

[File Handle]

On File Handle Said:

On Mark Rand Said:

BA is specified entirely in metric 🙂 6mm diameter and 1mm thread pitch for 0BA. Every subsequent size is 0.9 times the diameter and pitch of the previous one.

Rounded to the nearest thou for mere mortals, though.

Although based upon 0BA is based upon 6mm dia and 1mm pitch, isn’t the thread actually specified in fractions of an inch in the standard? It and the one it was copied from are perhaps, however, the only thread series based upon a mathematical and scientifically logical series?

As far as British Standards go, it looks like it’s actually specified in metric, though pretty much every UK book I’ve seen gives the imperial equivalents, as per Annex D.

It’s hard to get access to BS free these days, but libraries in some parts of the country do give free access via their library cards.
I think Northern Ireland and Lancashire are amongst them; Manchester allow access free if you visit, but sadly Derbyshire’s cards don’t have the facility.
This pdf may not be the most current, but I can’t see any replacement being much different

Bill

[Michael GilliganParticipant @michaelgilligan61133]

The item in the Bibliography should be an interesting read, if we can locate a copy.

At a mere 8 pages [much of which is usually padding] it seems  a bit pricey though.

 

MichaelG.

[Michael Gilligan]

On Michael Gilligan Said:

The item in the Bibliography should be an interesting read, if we can locate a copy.

At a mere 8 pages [much of which is usually padding] it seems  a bit pricey though.

 

MichaelG.

I failed completely; hopefully there is someone on here who can access British Standards via their library card.

The documents referred to in several other standards, some of which members might find informative. 😉

As Above BA threads

BSW parallel Threads

Metric 1   &   Metric 2

Unified 1   &   Unified 3  (Unified 2 was combined into 1 2007 edition apparently)

General Federal specs

All of the above may well be out of date.

Bill

 

[peak4]

On peak4 Said:

 

As far as British Standards go, it looks like it’s actually specified in metric, though pretty much every UK book I’ve seen gives the imperial equivalents, as per Annex D.

 

I was quoting Tubal Cain (and indeed many others). Looking at the standard, I think that is the first time I have seen a metric BA table. Which does leave the question, did TC get it wrong, was the standard initially specified in inches, or was he simply referring to the fact that most published data used inches?

[File Handle]

On File Handle Said:

On peak4 Said:

 

As far as British Standards go, it looks like it’s actually specified in metric, though pretty much every UK book I’ve seen gives the imperial equivalents, as per Annex D.

 

I was quoting Tubal Cain (and indeed many others). Looking at the standard, I think that is the first time I have seen a metric BA table. Which does leave the question, did TC get it wrong, was the standard initially specified in inches, or was he simply referring to the fact that most published data used inches?

Here you go; unfortunately the link to the reports I originally had saved now has a Cloudflare access problem (sounds familiar)
However, Archive.org does have the documents archived, which you can open and then save as a pdf, depending on the vagaries of you operating system.

British Association Small Screws Committee 1st Report, 1882

British Association Small Screws Committee 2nd Report, 1884

Whitworth’s 1841 paper is available online HERE

Bill

[Howard LewisParticipant @howardlewis46836]

I think that you will ,find the hexagon size for Unified fasteners is generally related to the nominal thread diameter, rather than the pitch.

So that, as an instance, a 5/16″ thread will have ta 1/2″ A/F hexagon, whether UNC or UNF.

Howard

[Mark RandParticipant @markrand96270]

It’s amusing to note the slight mathematical difference which disappeared when the inch was redefined (metricated?) to be exactly 25.4mm. From the second link:-

9. Again, it is to be remembered that the use of metric measurement to designate the pitch need not inconvenience English manufacturers who are desirous of cutting the screws in their lathes. For, as has recently been pointed out by Mr. Bosanquet,5 it is easy to cut a thread, whose pitch differs from one millimetre by an amount which may for all ordinary purposes be neglected (1/155300th), with a guide-screw based on the inch by the addition of a wheel of 127 teeth,

[peak4Participant @peak4]

Perhaps now an appropriate time to provide a link to Which Inch, a pdf I found on the Metrication Matters website.
I’ve not uploaded it previously, preferring to provide a link to the original location, but it looks like the URL has either been hijacked, or lapsed and been taken over.
The document now resides in My Documents gallery on this forum; copyright obviously remains with the author.

Fortunately some of the original Metrication Matters site is available via various snapshots on The Internet Archive

It you’ve not seen it before, the “Which Inch” pdf is worth a read.

Bill

[Michael GilliganParticipant @michaelgilligan61133]

Well done, Bill

… I’ve read it before, but never expected it to disappear !

Duly downloaded, thanks.

MichaelG.

.

P.S. __ after all the effort that was put-in over the years; that closing statement always amuses me. … Does anyone have an actual vacuum available ?  🙂

[Michael GilliganParticipant @michaelgilligan61133]

I am truly sorry, Bill … but I am not at liberty to share PD 6494

… I will however quote the introductory text, on the principle of ‘fair use’

 

MichaelG

[Michael Gilligan]

On Michael Gilligan Said:

Well done, Bill

… I’ve read it before, but never expected it to disappear !

Duly downloaded, thanks.

MichaelG.

.

P.S. __ after all the effort that was put-in over the years; that closing statement always amuses me. … Does anyone have an actual vacuum available ?  🙂

Unfortunately, it’s always going to be a problem with the internet; largely down to funding and who pays to keep websites up and running.
Sadly the author, Pat Naughtin, died back in 2011, after producing 100 newsletters and various other stuff, but it seems that it’s all gone, other than what’s on sites such as The Internet Archive, or Wikipedia, all of which need continuous funding somehow.
Even this forum is an example of that, where all the old albums are no longer visible.
Maybe I should start downloading the newsletters, but who would host them?

Here’s a TED Talk by the chap.

Edit; it looks like Michael and I were typing at the same time.
It’s good that the previous post and this one came out in the order they did, as it helps illustrate some of the points raised in the video.

Bill

[David LindquistParticipant @davidlindquist71920]

From the Wikipedia article: https://en.wikipedia.org/wiki/Carl_Edvard_Johansson#Johansson_and_the_inch

In 1912 C.E. Johansson undertook to make his gage blocks in inch sizes. At that time the U.S. inch was every so slightly more than 25.4 mm and the U.K. inch ever so slightly less than 25.4 mm. Johansson dealt with this by effectively deeming the inch to be 25.4 mm exactly. As his gage blocks became fundamental references, “industry associations” in the U.K. and the U.S. adopted 25.4 mm as the “standard industrial inch” (1930 and 1933 respectively.) In particular see reference 4 in the Wikipedia article.

 

David

[Michael Gilligan]

On Michael Gilligan Said:

On SillyOldDuffer Said:

On Michael Gilligan Said:

… but, I think the Whitworth thread form was widely adopted because engineers recognised:

1. its technical merits
2. its geometric elegance, and
3. all the effort that went into producing and standardising it

It was, and remains, a fundamentally good design … and Sir Joseph Whitworth was widely respected.

Bottom line … If you wanted a good form for screw-thread; why choose any other ?

It was [as intended] definitive.

MichaelG.

 

Not how I read the history.  Whitworth came up with something far cleverer than a mere thread – standardisation.  …

 

You are entitled to your ‘reading’ Dave, as I am to mine … but I am genuinely disappointed that you have strayed so far from the point.

We were discussing the Whitworth Thread Form, and Forms do not depend upon units of measure, or upon size; they are simply a shape.

MichaelG.

…

In my defence, I was talking about the importance of standardisation.  Whitworth defined a thread form in the measurement system of his time and country – inches.  Truly great idea except that inches were part of an inherently non-standard system.  Muddled because it’s members were decided trade by trade before it was realised there was a relationship between mass, length, time and amperes.

Whitworth’s innovation made shoals of non-standard threads obsolete, and no-one mourns them! In turn Metric made Whitworth threads obsolete, for the same reason.   I don’t think Whitworth cared about inches or his thread form – what he wanted was to reduce chaos.

Dave

[Michael GilliganParticipant @michaelgilligan61133]

Sorry, Dave … you miss my [perhaps obscure] point

The form is only about shape … all of the numbers are proportions not dimensions, and have no units of measure.

It’s rather like a vector file … make it any size you want.

MichaelG.

.

From my first response to Bill:

Edit: __ this diagram ‘says it all’

.

https://en.wikipedia.org/wiki/British_Standard_Whitworth#/media/File:Whitworth_Thread.svg

 

[Nigel Graham 2Participant @nigelgraham2]

There is a difference between standard and coherent (in ISO-ese) systems.

The units of length, including the inch, had been standardised otherwise Sir Joseph Whitworth could not have created his standard thread form.

Similarly with other dimensions, so although their systems were not mutually coherent, they were standard in themselves sufficiently by the late-19C to allow compound units that use those links between distance, time, etc. Hence to start analysing numerically, matters from steam-engine design to astronomy.

So Metric did not make BSW obsolete because the latter were non-standard. They replaced one set of existing standards by another. The origins of the two length systems were very different – respectively 18C geography and ancient trade practice – but that is beside the point.

 

It’s really only very recently that some arcane committee took what anyway were always really arbitrary units, chivvy them into coherence, define them in rather circular ways by things like wavelengths of light and each other, then give them and their compounds, people’s names to obstruct dimensional-analysis!

=====

People’s names…..

I used to quote certain measurements in [a negative number of] dB re 1V / µPa.

or… deciBels re 1Volt per µPascal.

So that’s three worthies: Bell, Volta and Pascal. (“re” is short for “referred to”.)

Expand it by one stage and you find a fourth scientist:

[number of] DeciBels re 1Volt / micro{Newton/square-metre}

Expand it fully, and there’s no room on the label.

Is all this really a fitting memorial to these pioneering physicists?

 

In case you are wondering, that lot is the standard “unit” for the sensitivity of a hydrophone.

 

[peak4Participant @peak4]

I have posted this link before; it seems that Whitworth proposed a decimal series of threads, still on inches of course rather than one based on 1/64th” etc.  See Column 1 of the table
It seems his idea didn’t take off, other than for rulers.

“It would be desirable that those establishments which may decide upon adopting the decimal scale should introduce rules having the inch divided into tenths and their subdivisions, which would soon become as familiar to the workman as the eighth scale he now uses.”

STANDARD DECIMAL MEASURES OF LENGTH. Manchester, 1857.

Bill

[Nigel Graham 2]

On Nigel Graham 2 Said:

There is a difference between standard and coherent (in ISO-ese) systems.

The units of length, including the inch, had been standardised otherwise Sir Joseph Whitworth could not have created his standard thread form.

[…]

[…]

 

Is all this really a fitting memorial to these pioneering physicists?

 

In case you are wondering, that lot is the standard “unit” for the sensitivity of a hydrophone.

 

Nice example, Nigel … but I must again take issue with a statement [which I have emboldened for clarity] about Sir Joseph Whitworth’s exquisite thread form.

The form is dimensionless, and would be identical at any size, or expressed any system of linear measurement units … be they microns, furlongs, or light-years … it is simply a shape.

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Michael is correct.

A thread FORM is merely the SHAPE of the thread and is not confined by a dimension of any sort.

Because Whitworth was working in a country where the inch was a standard dimensional unit, he set the standard using the Inch as the unit.

His standard thread FORM is one with a 55 degree angle, with the crest rounded by a proportion of the pitch. (Which is where a dimesion, other than an angle, comes into play)

In similar manner, Unified and Metric threads are of 60 degree angle with the crest flattened, again by a proportion of the pitch.

Unified thread FORM is used in Unified Coarse, Unified Fine, Unified Extra Fine, and Unified Special, in the same way that the Metric thread FORM is present in Metric Coarse, and Metric Fine systems.

It is just the pitch that changes, based on the diameter.

(In crude terminilogy, an equilateral triangle with the top chopped off)

A thread SYSTEM can be of any form, and of ANY pitch that the maker chooses.

(It could be argued that BA is an example, with a 47.5 degree angle,  with the “basic” 0 BA being 6 mm x 1mm pitch, with subsequent diameters and pitches being reduced by a factor of 0.9).

British Standard Pipe threads are of Whitworth FORM, but the pitch, although related (not proportionally) to diameter, does not follow the standard for attachment threads.

Brass threads have a Whitworth form, and are a constant 26 tpi, as are Cycle threads, (BUT they are of 60 degree FORM, like Unified and Metric).

A Left Hand thread could be of any FORM, but not necessarily conform to a STANDARD for a Right Hand thread, in terms of pitch. There are times when conforming to a standard pitch is needed, as in turnbuckles wher a similar right hand thread is used for the purpose of adjustment.

(But sometimes where a specially fine adjustment is need, the thread pitches may differ)

BSW threads are of Whitworth form, with the pitch related to the diameter.

RPS threads are also of Whitworth FORM, but do not conform to the British STANDARD Whitworth thread, on diameter or pitch.

As an example, FOR A PARTICULAR PURPOSE, and because it suited me, with no expectation that it would ever be repeated, I produced an unusual thread, both in FORM and pitch.

In this instance the depth and pitch determined the exact FORM.

(Being assymetric, was not a knuckle thread, and therefore, to which I cannot ascribe a title for the form)

It was produced using a 1/8″ diameter toolbit, with a depth of 0.0625″, with a pitch of 4 mm, to produce a flat topped thread with a semi circular root.

A TOTAL oddball, which surely, no one would want to set as a standard of either form or pitch.

Howard

[Nigel Graham 2]

On Nigel Graham 2 Said:

…
 

People’s names…..

I used to quote certain measurements in [a negative number of] dB re 1V / µPa.

or… deciBels re 1Volt per µPascal.

So that’s three worthies: Bell, Volta and Pascal. (“re” is short for “referred to”.)

Expand it by one stage and you find a fourth scientist:

[number of] DeciBels re 1Volt / micro{Newton/square-metre}

Expand it fully, and there’s no room on the label.

Is all this really a fitting memorial to these pioneering physicists?

 

In case you are wondering, that lot is the standard “unit” for the sensitivity of a hydrophone.

 

I see no harm in it.   What’s a good alternative for Volt?    ‘Potential Difference’ is clumsier and doesn’t really describe what nature is doing, so we might just as well celebrate Alessandro Volta’s major contribution to understanding electricity.

Forum members could be celebrated the same way: I suggest these units, the Duffer, Nigel, Morton, Jason and Gilligan:

• Gilligan – % strength of GoogleFu needed to find obscure patents, scientific papers and other internet references
• Nigel – scale of how difficult it is to learn a tricky new 3D-CAD package
• Duffer – % mistakes made per post that have to be apologetically corrected
• Morton – 1 bug per pixel
• Jason – one new model engine built per day.

Dave

[mark costello 1Participant @markcostello1]

So what thread form is stronger? I realize that butress or Acme would be stronger but how about “V” form threads?

[Author]

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