Speedometer Retainer - thread size please

[angelfj1]

Hello folks. I have a tach which has the early case which is held to the facia with a one-piece retainer plate. I need help identifying the threads on these retainer studs. I can't match them with any of my thread pitch gauges. The newer cases have studs with 8-32 threads, but the older case has heavier studs, like maybe size 10-??.

help!

 

[TR3driver]

They are a screwball metric thread, not found in any of the standard sets. Don't have the details handy, but I was planning to order a tap & die from MMC.

Might be M5x.75 but don't quote me on that.

 

[dklawson]

They are actually a more "obscure" thread. Like the tapped holes on SU electric fuel pumps they are "BA" threads. I believe the smaller size (close to 8-32) is size 3BA. The larger thread (close to 10-32) is 2BA.

Here's the Wikipedia link for information on the BA thread sizes. You can measure what's on the gauge and compare to the chart here:
https://en.wikipedia.org/wiki/British_Association_screw_threads

 

[Gliderman8]

OK, here goes.... I believe they are 8-36
No, not metric but a little used size.
It drove me crazy trying to find the right size when I installed my gauges. 8-32 was close, but not correct... 8-36 was a perfect fit.

 

[TR3driver]

Well, the ones I examined were definitely not BA, nor 8-36. I tried a 36 tpi thread gauge, as well as a 2BA tap, and neither one matched. The diameter is wrong, too.

But that doesn't mean they are all the same.

 

[Gliderman8]

I should have stated that they were for my '73 TR6. You are probably correct Randall in that earlier models used different thread sizes.

 

[dklawson]

You're right, they're not all the same. I know the later gauges (mainly the 2-1/8" ones) went to "inch" size studs with fine (but not common) pitches. Most of the gauges you find from the 1960s will have the BA threads. The only reason I have the few BA taps and dies I have is to make nuts and such for gauges and fuel pumps. I'm surprised that a '73 Smiths gauge (speedo or tach) would have switched to inch threads.

EDIT:
Randall, didn't you tell me several months ago that the gearbox connection thread for the speedo cable was 3/4-26? Prior to your info I'd always thought the thread was M19x1. I don't remember if you and I talked about the threads on the back of the speedo and cable tachs. I've always believed them to be M12x1 but after what you found about the gearbox end of the cable you've got me wondering if that's really supposed to be 1/2x26. Do you have any info on that?

 

[TR3driver]

I've always believed them to be M12x1 but after what you found about the gearbox end of the cable you've got me wondering if that's really supposed to be 1/2x26. Do you have any info on that?

Looks like M12x1 to me. I measured the diameter at .471" and the 26 tpi thread gauge is just a little bit too fine. 25 tpi is very close, might be right but my chart doesn't show anything close to .471" by 25 tpi.

However, M12x1 (.4724" by 25.4 tpi) is right there.

https://i258.photobucket.com/albums/hh260/TR3driver/untitled.jpg?t=1248411907

 

[dklawson]

Thanks Randall. I have a added a printout of your picture link above to my thread data files.

 

[TR6BILL]

They are definitely Metric. At least some Metric thumscrews I had fit perfectly. And, the little short brake pipes on the front calipers briefly switched over in 73 to Metric, then went back again. Ask me how I know. I have a pair of highly collectible pipes with the original BL tags on them, Metric. If anyone wants to make the perfect transition '73 into the ultimate show car, these are available for a huge sum of money. All of which I would gladly donate to charity.

 

[TR3driver]

I have a added a printout of your picture link above to my thread data files.

I'll be happy to send you the entire PDF file, if you would like to have it, Doug. (Or anyone else, of course.)

But there is a more complete version available (along with lots of other information about threads) at https://ssl.perfora.net/metricshop.com/tech/tic1e.htm

 

[TR3driver]

And, the little short brake pipes on the front calipers briefly switched over in 73 to Metric, then went back again.

Are you sure they went back? I knew the threads into the caliper changed to metric, late in 1972 (effectively 1973 model year); but I was under the impression they remained that way through the end of production.

The mounting holes also changed to metric, which is why the late mounting bolts are so expensive (metric shanks with SAE threads).

 

[dklawson]

What are we talking about now, brakes or gauges being metric?

I have never seen any true metric threads on Smiths gauges. If you do have gauges with metric threads on them, please let me know what year the car/gauges are and what metric size the threads are. I try and keep up things like that for no really good reason.

Randall, I'd love to see the PDF you have. I appreciate the link to Maryland Metrics. I occasionally order stuff from them for work.

 

[dklawson]

Thanks Randall. I received your thread table. I'll add it to my files.

I've given some more thought to the possibility of metric studs on the Smiths gauges in light of TR6Bill's comments. If the studs on the gauge were 2BA (which is close to 10-32 but not quite right) then an M5 nut would fit those threads very well. The 2BA thread is 0.185 OD with a pitch of 31.35 threads/inch. A standard M5 is nominally 0.197" OD with a pitch of .8mm (31.75 threads/inch). The slight mismatch in the thread pitch would be offset by the larger diameter in the nut. A 10-32 nut MAY fit a 2BA stud but probably not since it is smaller in diameter and has a greater pitch error.

 

[angelfj1]

My '2BA' taps and die arrived today and the die is a perfect fit on these retainer studs. I was able to chase the threads easily with thumb and index finger - no binding or resistance. Could there have been more than one thread size used?

 

[dklawson]

Yes indeed. As was mentioned earlier in this thread there were a couple of different thread sizes over the years.

Like you found, the 2BA thread was used on many early gauges. I know I've seen some later gauges (late 1970s) that were "inch" (UNF) threads.

 

[TR3driver]

And I double-checked yet another large gauge (a speedo this time) from a pre-1960 TR3/A; to find that it's threads are definitely not 2BA nor SAE. A 2BA die immediately starts to cut, and using a 2BA tap as a thread gauge shows a substantial difference in pitch. These are definitely earlier gauges than the one visible in Frank's photo above.

Still looks like M5-.75 to me. But for some reason MMC has quit carrying that size, and I haven't put in an order to MSC yet.

Doug, these gauges say "British Jaeger", not Smiths; although I believe Smiths owned at least most of British Jaeger Instruments at the time.
https://www.britishcarcouncil.com/history/smiths.html

 

[dklawson]

Somewhere on the net I found a PDF summary/history of Smiths & Sons that went on to become Smiths Instruments. I wish I could provide a link... I have a printout from the web site somewhere at home.

Of interest was the connection between Jaeger and Smiths. Jaeger was a continental gauge/instrument firm when Smiths started making instruments for British cars. Smiths and Jaeger entered in to a joint operating agreement of sorts and at some later date severed their agreement. Smiths continued to mark some of their designs as "British Jaeger" to distinguish them from those produced by Jaeger on the continent. You will occasionally see instruments marked as just "Jaeger" but inside they will be totally different from what you're used to on British cars. Inside, most British Jaeger gauges of the 1960s and 1970s will be identical to those marked Smiths. I don't know if that applies to cars from the later 1940s and 1950s.

Of equal interest, this document discussed the relationship between Lucas and Smiths. (Again from memory) Smiths and Lucas entered into a gentleman's agreement about which company would make which type of automotive electrical equipment so they would minimize their direct competition with each other. I don't understand the limits of their agreement as Smiths made instruments and things like ventilation blowers... while Lucas made Ammeters and most of the other wiring devices... but not motors. Anyway, their agreement eventually dissolved.

I'm not sure when Smiths & Sons stopped making timepieces.

TMI, but I still find it interesting.

 

[TR3driver]

Doug, did you read through the page I linked to above? It may be the same page you are thinking of (or a copy of it).

However, it is fairly explicit that there were (at least) three different companies named Jaeger, one French, one English, and one Swiss, with all sorts of agreements and sharing of patents and technical information between the three of them. Smiths acquired 75% of "Ed. Jaeger (London) Ltd." in 1927; and then it was renamed "British Jaeger Instruments Ltd." in 1931.

Lots more, including Smiths becoming sole distributor in the UK of VDO and French Jaeger instruments in 1954. Their agreement to share patents with French Jaeger was apparently terminated in 1961, but the electric clock patent had already expired and Smiths continued to use it.

According to https://www.smiths-clocks.co.uk/sm-hist.htm, Smiths quit building clocks "for the domestic market" in 1979. By that time, they had split into "Smiths Industries Clock Co." and "Smiths Industries Watch Co.".

 

[dklawson]

Sorry Randall... when I made my last post I was rushing to finish typing as I was leaving work for the day. (Or is that leaving not-work since I was on the web?). The link you provided probably is the one I was remembering.

I did not remember the third link to a Swiss Jaeger company, thanks for pointing that (and the specific dates) out. I don't think I was too far afield considering I was typing only what I remembered.

To me, Jaeger is a German name pronounced "Yay-ger", it is the word for "hunter". The French firms using this name have given it a French pronunciation "jay-jerr". In my job I have run into two interesting twists related to these instrument companies.

There is a French Jaeger firm operating today that makes industrial electrical connectors. (Sort of a modern version of the Amphenol/Bendix connectors used on military products). There is also a connector company in Europe called "Hypertronics" who make a nearly identical line of electrical connectors. Hypertronics is owned by a parent company "Smiths". I believe this Smiths was once part of the U.K. instrument maker. I don't know if the French Jaeger connector company is related to the firm that used to make gauges but it's interesting to think that there are Jaeger and Smiths firms who MAY be descendants of the instrument firms competing with each other in a very different industry.

I remember reading a lot of the history of VDO also but somehow missed their connection to Smiths. Thanks also for pointing that out.

Well, this has certainly taken us far afield of the original subject of this thread. Randall, I apologize for not reading the pages in your link before my last post. As recognition that the original question was about thread types on Smiths gauges, I'd like to close this post by saying that I know the threads changed over the years and fortunately for me, most have had UNF threads or BA threads that I have taps and dies for.

EDIT:
One more OT thing I wanted to mention. My father has been deceased for quite a while. One of his possessions that I inherited and love is his "service clock" presented by Monsanto after he'd worked there for more than 30 years. It's an Atmos clock made by Jaeger-LeCoultre. These are fascinating clocks that work by temperature change. You never wind them and they have no batteries.
https://www.atmosclocks.com/