What thread is this?

[Peter GiddenParticipant @petergidden66722]

Hi All

Apologiesin advance if i have posted in the wrong forum.

I need to identify the thread in the photo. It belongs to a coolant temperature sensor for BMW Mini / Peugeot / Citroen engines, and was designed to replace a plastic bleed screw.

Outside diameter of thread is 8.8mm

Pitch is close to, if not exactly, 1.5mm.

Thanks for looking.

[Peter GiddenParticipant @petergidden66722]

[Brian WoodParticipant @brianwood45127]

Hello Peter,

I don't quite know what you expect, you describe the pitch and O/D which is in itself a description of the thread. If it is a thread name you are looking for I really can't help you

Incidentally, the thread looks remarkably like those in current use on the larger Sparklets CO2 gas refill cylinders, which of course are not compatible with our older device with regular gas threads, for which I also had a spare cylinder. To add insult to injury, those are not exchangeable either. Progress? I wonder!

Sorry I can't be more helpful and welcome to the Forum by the way. We usually tell new members they can get all the answers to their questions here—-hey ho !!

Regards

Brian

[John HaineParticipant @johnhaine32865]

The pitch is probably 1.5 mm exactly as it seems rare to use odd pitches. The nominal outside diameter is probably 9 mm but the thread form looks odd being more square than triangular. Looking online similar items are generally M12x1.5 with conventional thread form.

[Clive FosterParticipant @clivefoster55965]

Peter

As its an automotive application and made to screw into plastic its almost certainly a special.

Flat top suggests its either ACME or Metric Trapezoidal form, see **LINK** , for brief details.

Unfortunately its too small for the standard ranges given. I'd guess either 9 mm nominal full diameter with 1.5 mm pitch in metric trapezoidal or stub metric trapezoidal. Too small to be a stub ACME version of the 1/2" x 16 TPI thread used for R134a gas canisters.

Found this useful link for thread calculations **LINK**.

Home page has links to lots more calculators **LINK**.

[Neil WyattModerator @neilwyatt]

Hello Peter,

Could it be a special intended to stop people fitting aftermarket versions?

To me it looks like a square thread.

Do you need to finds something that fits it, or copy it?

Neil

[pgk pgkParticipant @pgkpgk17461]

There is a metric trapezoidal thread 9mm x 1.5 with the major diameter range from 9.0mm-8.85mm that fits this description.

**LINK**

pgk

[Clive FosterParticipant @clivefoster55965]

Reckon pgk pgk has nailed it.

Another link for my Engineering Data bookmarks folder! Goes to show that you need more than one source as my usual go to doesn't show all the ones in that link. Most but not all.

Clive

Edited By Clive Foster on 18/02/2018 12:00:45

Poxy spell check, twice.

Edited By Clive Foster on 18/02/2018 12:01:28

[Tim StevensParticipant @timstevens64731]

I suggest that it is very likely to be the 9 x 1.5 Trapezoidal thread identified in the link from pgk pgk. Motor cars are mass produced, with components from all over the world, so if possible everything is built to a standard of some sort. This means that cutting tools, gauges, and other checking kit is readily available, rather than 'special', and so one-off, expensive, and hard to replicate if damaged or an alternative supplier is sought.

It is also the case that coarse, and squarish threads like this are preferred for plastics as the properties are quite a lot different from the metals with which we are more familiar. So, a metal replacement for a plastic part has a plastic-style thread.

Cheers, Tim

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