M1.7 – what is the history behind it?

[Another JohnSParticipant @anotherjohns]

I have a friend looking for a M1.7 tap – which I don't have.

But, it brings up a question I have had for a long while – what is the history of M1.7, as opposed to M1.6 (ISO and DIN standards). The local shop can order in M1.7 screws of certain lenths/materials, and M1.6 in other lengths/materials.

I put it down to old stock – probably not a lot of metric users, as I'm in the 2% or less of the local ME club that chooses to build in metric.

Any background? Merci – John.

[Another JohnSParticipant @anotherjohns]

[jason udallParticipant @jasonudall57142]

Well in production we once supplied to customer order parts tapped M 1.6.. to mate with M 1.8 male

This was for a purpose of their own.
( not explained to us)…
At the time I was lead to believe the pitch was simular enough that the m1.6 m1.7 m1.8 was almost more a “fit” issue?rather than size.

[MuzzerParticipant @muzzer]

Could M1.7 also be known as 10BA??

[Another JohnSParticipant @anotherjohns]

Checking further, the pitch is the same between M1.6 and M1.7 (At least according to 1 reference)

Murray – interesting thought about metricizing 10BA as M1.7 – pitch is incredibly close, (0.351 vs 0.350). Different thread form, but maybe, so what??

Jason – you are right – all the same pitch.

Emailed my friend, who is a BA-aholic, and suggested he try 10BA and see what happens. (It's for an Aster locomotive kit out of Japan)

John.

[jim’Participant @jim11037]

all you need to know about metric threads

**LINK**

[David JuppParticipant @davidjupp51506]

The BA option sounds sensible. In the parts manual for an old Olympus camera, all screws were described in mm – study revealed they were all BA equivalents.

[Neil WyattModerator @neilwyatt]

Why M1.7?

The most useful series of fixings (or anything needed in a wide range of sizes) go up in steps of similar size, so that whatever your 'ideal' size is there is always a standard (or 'preferred&#39 size nearby.

The best example is resistors, which go up in odd values, or at least they seem odd until you realise that the values are spaced so that they go up in steps more or less regular steps of 1.5 times the previous value (at 20% tolerance). For higher tolerances they go up in smaller steps, always chosen so that there aren't any gaps between the tolerance bands.. This minimises the number of values they need to make, means there are no 'rejects', and simplifies the design process.

The steps can be any size. For BA fixings the step is such that as you go down the series each size is 0.9 times the previous one – quite close together which is why just the even sizes are more commonly used.

Other examples are things like A-series paper where A4 is twice the area of A5.

For ISO metric things there are the R5, R10, R20, R40 and R80 series which break down each 'decade' (from 1-10 or 100-1000 for example) into steps of 10, 20, 40 or 80 roughly even-proportioned steps.

Engineering ignores these steps so most metric screws you come across are rounded to the figures: M1, M1.5, M2, M3, M4, M6, M8, M10.

The final answer to your question is that M1.7 is the most useful size between 1.5 and M2.

Neil

[AjohnwParticipant @ajohnw51620]

There is a site that lists metric threads that might be of interest. Topsy springs to mind.

**LINK**

John

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[BazyleParticipant @bazyle]

Since you said it was for an Aster loco, Japanese made but I think designed in Switzerland, it will depend on the designer and whether he is a hands-on practical man or an academic CAD jockey. Wanting to meet scale (of a sort) the designer will have found that M1.7 is the required size and exists in the tables. Being Swiss every possible small screw will be available locally so he just specifies it no problem. A hands on man would have known what was more commonly available and adjusted. The Far East like to follow instructions so will not suggest an alternative and just build to print at slightly extra cost.

How did the friend determine it was 1.7mm. Either he measured the diameter and quoted that not actually differentiating it as metric or BA, or he has a parts list, (quite likely as many are sold as kits) that specifically declares it as M1.7 therefore not BA.

Edited By Bazyle on 12/11/2015 13:43:52

[KWILParticipant @kwil]

There are some strange metric thread uses. Japan uses M2.6.

Lost a locking screw on a S/S mechanical vernier, too quickly measured it as M2.5, made one did not fit!!

Measured it more carefully, made one as M2.6, worked a treat

No logic as to why it was M2.6

[AjohnwParticipant @ajohnw51620]

Posted by KWIL on 12/11/2015 15:49:01:

There are some strange metric thread uses. Japan uses M2.6.

Lost a locking screw on a S/S mechanical vernier, too quickly measured it as M2.5, made one did not fit!!

Measured it more carefully, made one as M2.6, worked a treat

No logic as to why it was M2.6

If you look at the ISO extended metric threads here you will see there is nothing odd about M2.6 at all

**LINK**

On the other hand they have been rationalised and I believe this is one is more up to date unless JIS has dropped some of theirs.

**LINK**

It pays to check dia and pitch on Japanese microscope. German too.

John

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[Clive HartlandParticipant @clivehartland94829]

Of interest, while working for a very well known Swiss Company they did in mid stride opt to use the new Din Norm on threads so we ended up with several different threads used on instruments and it was particularly annoying to find small threads on items that you had used say 1.7 suddenly were 1.6.

We also used a lot of non standard threads as we needed very fine movement for adjustment purpose on bubbles etc. We also found that the taps and dies for these threads extraordinarily expensive. A 5 start thread for eyepices at £280. Some large diameter very fine threads I made myself as we would not have got the purchase through the finance dept.

Clive

[egaParticipant @ega]

John W 1:

"There is a site that lists metric threads that might be of interest."

Thanks for reminding me of this useful site – it feels odd that one goes to the US for such a comprehensive list.

[KWILParticipant @kwil]

John,

I was well aware that it was an ISO thread, just odd they chose it!

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