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M4 x 0.75mm pitch CSk machine screws

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vintage engineer22/08/2019 17:33:24
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Anyone know a supplier of these please?

JA22/08/2019 17:47:51
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This is not a standard size. M4 x 0,70 is Metric Coarse.

JA

not done it yet22/08/2019 18:04:31
3476 forum posts
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Are you sure the thread is not 3BA?

vintage engineer22/08/2019 20:40:37
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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 IoM22/08/2019 20:45:56
653 forum posts
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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.
JasonB22/08/2019 20:48:17
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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.

Meunier22/08/2019 20:52:38
256 forum posts
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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 Dayman22/08/2019 21:08:38
1643 forum posts
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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 engineer22/08/2019 21:12:05
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It's for a pair of Cozette Blowers which are French, which is why it's an odd metric size!

Keith Long22/08/2019 21:44:17
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Tracy tools list the taps and dies for these if you don't fancy screwcutting them.

Jeff Dayman22/08/2019 22:12:28
1643 forum posts
42 photos

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 122/08/2019 22:52:13
2096 forum posts
144 photos

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.

Andrew Johnston22/08/2019 23:08:09
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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 engineer22/08/2019 23:15:21
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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

Nicholas Wheeler 122/08/2019 23:58:59
276 forum posts
16 photos
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.

KWIL23/08/2019 07:24:35
3127 forum posts
57 photos

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

not done it yet23/08/2019 08:56:48
3476 forum posts
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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.smiley “Ally Barber” would gladly supply a million from China. Not so good a price, or availability, if one only wanted four or five!

Neil Wyatt23/08/2019 09:33:37
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GIYF.

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

Not a cheap option with shipping, I guess.

Neil

Lainchy23/08/2019 09:34:28
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134 forum posts
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Drop CW Fasteners a question. They stock all manner of fastenings.... **LINK**

Michael Gilligan23/08/2019 09:40:01
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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.smiley “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.

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