Smiths mounting nut size(s)

[stugilmour]

I lost one of the knurled nuts to mount my Smiths tach.

Are the nut sizes different for the major and minor gauges? I might have a nut from a small gauge if I dig around a bit, but I am sure I don’t have one for a large gauge if it is a different size.

What are the thread size(s) used? I see references on eBay to M4, M5 and M5 x 0.75, which should be easy to find locally. I guess I was assuming it must be much more difficult than that! Maybe metric for later ‘80’s or current reproduction gauges? Another listing calls up 3BA for a Cortina, but doesn’t mention if it is for a major or minor gauge? Another says this is for the small gauge, kinda implying it is probably not for the late ones. One listed for a Maserati looks promising ’cus I would go a lot faster this those.

Any help appreciated. Shipping literally triples the cost of the darn things, so sure want to get it right.

Stu in Canada

[ericbushby]

The nut size is 3BA. I just make some when needed, This is certainly correct for the Speedo and Tachometer. I thought they were all the same.
Eric in Burnley
1967 S3SE DHC

[stugilmour]

Thanks Eric. That’s easy to get now. Will be interesting when I get my dash out, as I have a stock gas gauge and a new reproduction style Smiths voltmeter to check threads on. Perhaps the new gauge will be metric.

Stu

[ericbushby]

Hi Stu
That will be useful to know. If they are different it would be good to know. Of course everything should be metric by now but maybe historic stuff is still true to the original.
I was brought up on BA threads for electrical and instrument work and metric for everything else. That was a long time ago now. I am talking about the 1950`s.
Cheers
Eric in Burnley

[DavidLB]

I think that they have changed the thread on newer gauges david

[Donels]

Amazing this web site! Following this blog I purchased some nuts to replace std nuts that had been used on some gauges. EBay purchase from EMBERTONIMPERIAL.COM. Yes they are 3 BA which I believe is actually a metric thread so perhaps everyone is correct. The large and small refer to the outside diameter of the nuts as they come in two sizes, who knew?

[David1953]

I have two different threads on my gauges.
As this was discovered lying upside down and picking the wrong one up from where I had dropped them, I could not now say which went where. But I suspect the age of the gauge rather than the size makes the difference.

[Billmack]

Agreed with David. That nut can be found at any british car junkyard. Not at all lotus specific

[Sadbrewer]

I lost one of the knurled nuts to mount my Smiths tach.

Are the nut sizes different for the major and minor gauges? I might have a nut from a small gauge if I dig around a bit, but I am sure I don’t have one for a large gauge if it is a different size.

What are the thread size(s) used? I see references on eBay to M4, M5 and M5 x 0.75, which should be easy to find locally. I guess I was assuming it must be much more difficult than that! Maybe metric for later ‘80’s or current reproduction gauges? Another listing calls up 3BA for a Cortina, but doesn’t mention if it is for a major or minor gauge? Another says this is for the small gauge, kinda implying it is probably not for the late ones. One listed for a Maserati looks promising ’cus I would go a lot faster this those.

Any help appreciated. Shipping literally triples the cost of the darn things, so sure want to get it right.

Stu in Canada

Try these people...they might be prepared to put a small number in the mail.
https://maccmodels.co.uk/product-catego ... s/ba-nuts/
or these
https://shop.imperialnutsandbolts.com/p ... d-washers/