M4 x 0.75mm pitch CSk machine screws

[vintage engineerParticipant @vintageengineer]

Anyone know a supplier of these please?

[vintage engineerParticipant @vintageengineer]

[JAParticipant @ja]

This is not a standard size. M4 x 0,70 is Metric Coarse.

JA

[not done it yetParticipant @notdoneityet]

Are you sure the thread is not 3BA?

[vintage engineerParticipant @vintageengineer]

I know!!!

Posted by JA on 22/08/2019 17:47:51:

This is not a standard size. M4 x 0,70 is Metric Coarse.

JA

[Frances IoMParticipant @francesiom58905]

It was used – I have a tap (French made or labelled I think) + possibly a die among the pile of ‘it may be needed sometime’ items.
3 BA is fairly unusual – the odd BA sizes tended to be used by electrical industries that did not want consumers to fix or access the innards or organisations that wanted to discourage employees ‘borrowing’ a few fixtures for home use.

[JasonBModerator @jasonb]

I seem to remember a thread where someone wanted the same, they were used to hold some sort of panels, can't find it at the moment.

[MeunierParticipant @meunier]

It wasn't fixing light switch/power socket face-plates to pattress boxes, was it ?
DaveD

Edited By Meunier on 22/08/2019 20:54:25

[Jeff DaymanParticipant @jeffdayman43397]

Some idea of the application would help responders offer some remedial ideas.

If they are for panels in sheetmetal work, and only a few threads, there may be ways to use more available fasteners.

.75 mm pitch ( .0295" pitch) is very close to 34 tpi (.0294" )) . If you have a lathe than can cut 34 tpi you could make your own screws.

34 tpi (.0294" pitch) is close to 32 tpi (.0312" pitch) , only .0017" difference in 32 to 34 pitch, and 4.0 dia is .157". A stock #8-32 machine screw is .164 dia x 32 tpi. If not too many engaged threads are involved you could probably overtap the holes (if tapped) #8-32 and use #8-32 screws which are widely available in many materials, lengths, and head styles.

You could probably overtap the holes (if tapped) M4 x 0.7 and use M4 std screws, again if not too much thread engagement is needed. M4 are also available in lots of materials lengths and head styles.

If you can find some 3BA screws you could probably use them although their pitch is nominally 0.73mm not 0.75 so if there are a lot of engaged threads the screws might jam.

If you ever need to replace the screws in future years you might be glad you used #8-32 or M4 x 0.7 – BA screws are less and less available, it seems.

Edited By Jeff Dayman on 22/08/2019 21:09:18

Edited By Jeff Dayman on 22/08/2019 21:09:36

Edited By Jeff Dayman on 22/08/2019 21:11:54

[vintage engineerParticipant @vintageengineer]

It's for a pair of Cozette Blowers which are French, which is why it's an odd metric size!

[Keith LongParticipant @keithlong89920]

Tracy tools list the taps and dies for these if you don't fancy screwcutting them.

[Jeff DaymanParticipant @jeffdayman43397]

Are the threads in castings, bar, sheetmetal? (not familiar at all with Cozette blowers)

How deep / how many threads are there in the material?

What is the material the threads are in?

How many screws / holes are there?

[Les Jones 1Participant @lesjones1]

I agree with the others that they are probably 3BA. This is one source on ebay. but there is than one match searching for "3BA screws.

Les.

[Anonymous]

A 4 x 0.75mm pitch thread was part of the old French standard for metric threads specified by the Comite de Normalisation de la Mechanique. Threads from 6mm diameter upwards conformed to the ISO system. The old French standard below 6mm has now been replaced by the ISO system.

Andrew

[vintage engineerParticipant @vintageengineer]

Yes I agree. Working on early french cars has made my collection of metric taps and dies bigger than all my other taps and dies. I have 5 different size M10 taps!

Posted by Andrew Johnston on 22/08/2019 23:08:09:

A 4 x 0.75mm pitch thread was part of the old French standard for metric threads specified by the Comite de Normalisation de la Mechanique. Threads from 6mm diameter upwards conformed to the ISO system. The old French standard below 6mm has now been replaced by the ISO system.

Andrew

[Nick WheelerParticipant @nickwheeler]

Posted by Keith Long on 22/08/2019 21:44:17:

Tracy tools list the taps and dies for these if you don't fancy screwcutting them.

Is anyone really going to screwcut such a thread when they can buy taps and die?. Anyone who gets work done, that is.

[KWILParticipant @kwil]

Yes is the answer, it all depends upon how many items you need.

[not done it yetParticipant @notdoneityet]

Posted by KWIL on 23/08/2019 07:24:35:

Yes is the answer, it all depends upon how many items you need.

I know what you mean. “Ally Barber” would gladly supply a million from China. Not so good a price, or availability, if one only wanted four or five!

[Neil WyattModerator @neilwyatt]

GIYF.

http://www.classicandexotic.com/store/p-3865-m4-075-screw.aspx

Not a cheap option with shipping, I guess.

Neil

[LainchyParticipant @lainchy]

Drop CW Fasteners a question. They stock all manner of fastenings…. **LINK**

[Michael GilliganParticipant @michaelgilligan61133]

Posted by not done it yet on 23/08/2019 08:56:48:

Posted by KWIL on 23/08/2019 07:24:35:

Yes is the answer, it all depends upon how many items you need.

I know what you mean. “Ally Barber” would gladly supply a million from China. Not so good a price, or availability, if one only wanted four or five!

.

I may be wrong, but I think KWIL was answering the question by Nicholas Wheeler 1

[quote] Is anyone really going to screwcut such a thread when they can buy taps and die?. Anyone who gets work done, that is. [/quote]

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 23/08/2019 09:33:37:

GIYF.

http://www.classicandexotic.com/store/p-3865-m4-075-screw.aspx

Not a cheap option with shipping, I guess.

Neil

.

I wonder what the tolerances are, on those rather impressively specified dimensions

MichaelG.

.

M4-0.75 Screw as used on Hispano Suiza J-12.

Material: Steel
Finish: Natural
Thread: M4-0.75 x 15.75
OAL: 27.59mm
Shoulder: 8.5mm
Length under head: 23.84mm

[not done it yetParticipant @notdoneityet]

Posted by Michael Gilligan on 23/08/2019 09:40:01:

Posted by not done it yet on 23/08/2019 08:56:48:

Posted by KWIL on 23/08/2019 07:24:35:

Yes is the answer, it all depends upon how many items you need.

I know what you mean. “Ally Barber” would gladly supply a million from China. Not so good a price, or availability, if one only wanted four or five!

.

I may be wrong, but I think KWIL was answering the question by Nicholas Wheeler 1

[quote] Is anyone really going to screwcut such a thread when they can buy taps and die?. Anyone who gets work done, that is. [/quote]

MichaelG.

Mine was just a tongue in cheek reply referring right back to the start of the thread, there being no reference for anything else.

Just shows how things can easily be misconstrued – like three separate suggestions (in three separate sentences) all being assumed to be intimately connected when they were most certainly not!

[JasonBModerator @jasonb]

If there are more than you fancy making yourself then someone like Historicthreads may be able to run a small batch, expect their CNC machines would also hit the tolerances of the screws Neil linked to and would actually be CSK too.

Edited By JasonB on 23/08/2019 10:28:42

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 23/08/2019 10:27:31:

If there are more than you fancy making yourself then someone like Historicthreads may be able to run a small batch, expect their CNC machines would also hit the tolerances of the screws Neil linked to and would actually be CSK too.

.

Neil's link included no tolerances

[Author]

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