Gauge Thumb nut

[JeffW]

Hi

Does anyone know the size of thumb nut for the Temp gauge bracket? Mine disappeared but I can't find any listing which one is the correct size.

Thanks

Jeff

[mole42]

Do you mean the one on the back of the temperature gauge? I don’t know the exact thread but it’s an oddball- not metric, not BA. Maybe worth a phone call to the guys in Wales that make Smiths instruments?

[JeffW]

Yes that one - I thought something was amiss when none of my spares fit!

Thanks for the tip, will give them a call.

Jeff

[JOHNS]

I checked mine and a 5/32" x 36 UNF die fits so I suppose that is 8-36

[SteveD]

Is this what you need?

https://www.ebay.co.uk/p/2152131163?...RoCa_8QAvD_BwE

Steve

[JeffW]

I checked mine and a 5/32" x 36 UNF die fits so I suppose that is 8-36

Thanks. I spoke to Caerbont in Wales (Smiths) but they only said the current one is M4. I have read other posts saying in the 'mid-70's' Smiths changed from the old Imperial to M4, but Caerbont did not have any idea what the old one was as they don't have the part number.

I found this site selling '3ba' knurled nuts for Smiths gauges (https://www.ukmgparts.com/product/mg...all-3ba-17h932) as the predecessor to the M4 version, so took a punt and ordered some. I may be wrong though!

Jeff

[trunt]

I can confirm the change.. I had a set of instruments from a mk1 and 73 mk2 and had all of the thumb nuts from both in a bag. When I came to assemble them some fitted and some did not.. if I recall the knurled edges were different so i was able to tell the difference. One type had a crosshatch knurl, the other a straight line knurl.. can’t recall which was which..

Terry

[JeffW]

Is this what you need?

https://www.ebay.co.uk/p/2152131163?...RoCa_8QAvD_BwE

Steve

Hi Steve

Coincidentally, yes. Same part number as I ordered from the MG place, so I think those are (hopefully) the ones.

Jeff

[JeffW]

I can confirm the change.. I had a set of instruments from a mk1 and 73 mk2 and had all of the thumb nuts from both in a bag. When I came to assemble them some fitted and some did not.. if I recall the knurled edges were different so i was able to tell the difference. One type had a crosshatch knurl, the other a straight line knurl.. can’t recall which was which..

Terry

Thanks Terry, I will post pictures of what I get to compare!

Jeff

[JOHNS]

My car is a late '77 and it is definitely not 3 BA. The only die I could run was an 8-36 which is UNF. 8-32 is a UNC thread

[JeffW]

My car is a late '77 and it is definitely not 3 BA. The only die I could run was an 8-36 which is UNF. 8-32 is a UNC thread

Oh dammit.

I can't find any knurled nuts listed that are 8-36. I guess I will have to find a regular nut to use.

Thanks
Jeff

[JOHNS]

My car is a late '77 and it is definitely not 3 BA. The only die I could run was an 8-36 which is UNF. 8-32 is a UNC thread

I never thought for a minute that being a 77 British car mines could be metric but I just checked. Indeed it is M4. The thread pitch is the same as 8-36 at 36 TPI and that is why the 8-36 die fitted

[JeffW]

I never thought for a minute that being a 77 British car mines could be metric but I just checked. Indeed it is M4. The thread pitch is the same as 8-36 at 36 TPI and that is why the 8-36 die fitted

Right, then that lines up with the MG site selling the old versions - same statement on the eBay seller too:

These nuts were fitted from about 1960 until at some point in the mid 1970s these were supplied in both large and small diameters... At a point in mid 1970s smiths changed to M4 thread but they did not change the part number of the nut which does help much. The M4 nut was used from mid 1970 and this thread is still being used on the new gauges.

Mine is 1976 and definitely not M4.

Finger's crossed it's the 3ba!

Thanks
Jeff

[trunt]

I just dug out my bag-o-bits and it had 6 nuts with crosshatch knurles these did not fit my 73 instruments.. so I would guess that the early BA ones are crosshatch and later ones are straight knurl.

maybe someone can confirm that it -- may be a handy clue for others?

Or maybe its just a production difference in the knurling!!

Terry

[JeffW]

Pictures attached - 1 from MG site (3ba, cross-hatched knurl) and one from ebay seller, which has straight knurls...