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MG TD TF 1500 - Speedo Nuts

Can someone please tell me what size nuts are used on the speedo and tach retaining brackets? I need to source 5 ea. Moss offers them at $10 per nut!
Corey Pedersen

Corey--When I rebuilt my TF I found a some of the instruments nuts missing. I used nylon nuts available at most any hardware store (i.e. Ace hardware). Since there isn't a lot of stress on these they work just fine. I have removed the instruments a couple of times and, just as a precaution, I replaced the nylon nuts (quite cheap in price). On a couple of the instruments I perhaps went overboard by adding some lock washers. I also made sure that the nylon nuts were in the more accessible areas (not all that many) so that I can take a look at them once in a while for security. I have yet to find any of them loosened.

Larry
LD Kanaster

Thx Larry. Sounds like a nice solution!
Corey Pedersen

I thought thry were 2BA ( or 4BA ?)
I seem to remember using both when working on a TF dash
Don Harmer

I looked at my speedometer.
The nuts are knurled brass thumb nuts. They are 1/2" OD by 5/32 thick.

The thread appears to be 2BA.

Now 2BA is very close to 10-32. The BA thread form is however different, I believe th angle is around 42 degrees not the 60 of UNF threads.

I was able to run a 10-32 SCREW through the thumb nut.
I was not able to run a 10-32 NUT down the speedo screws.

I cant find my 10-32 die or I would have tried it on a bit of thread to see how much it cleaned up the threads.

I think the suggestion to use Nylon nuts is good. They will do no damage and could expand just enough to work.

Jim B.
JA Benjamin

If you happen to have a 2BA tap, and I guess I will have to buy one on my next order, here are some suitable substitutes form McMasters.

http://www.mcmaster.com/#thumb-screw-nuts/=kmswpq

You would either need to run a 2BA tap through them.

Jim B.
JA Benjamin

Jim - The 2BA thread count is 31.4. Are you sure that you were using a 10-32 nut and not a 8-32? The diameter of a 2BA screw is 0.1850 while the diameter of a 10-32 screw is 0.1900. I have always found that a 10-32 nut will screw right down on a 2BA screw with a sloppy fit. You can find a chart of all the standard threads in the Other Tech Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ By the way, that chart is courtesy of Don Harmer, many years ago, which found its way on to many other newsletters and finally on to my web site by permission - thank you again Don, that has been an invaluable source of thread information. Cheers - Dave
David DuBois

Are you sure that you were using a 10-32 nut and not a 8-32?
Yes definately 10-32 nuts were tight. its the 47.5 degree angle thats doing it.
I did try two different boxers of nuts also.

Its not that I could not thread it but the force was more than I wanted to use.

Jim B.
JA Benjamin

I think that I may have found the answer - from a post in 2004 regarding the mounting studs on the speedometer "The original thread is 5 mm x 0.75". This would explain the difficulty threading a 10-32 nut on the stud (to see how a 10-32 nut fits on a 2BA stud, try threading one on the power terminal of the fuel pump - the extra 0.005 size of the nut negates the effect of the 47.5° thread angle). Cheers - Dave
David DuBois

Hi All,
I don't know if this has come up before. If you check BA sizes you will see that OD and pitch come up as exact Metric sizes and in my toolroom data sheet the tap drill sizes also come up metric.
The BA series was used in the UK mainly by Electrical Engs just to confuse us Mech Engs.In the 1950's when I served my apprenticeship the UK used Imperial so finding Metric drills was difficult,now the opposite is true, finding Imperial tools is done in second hand shops(stores).
Out of interest,the terminal nut on spark plugs is BA and fits either the main panel or instrument nuts on the TF (cant remenber which),
Ray TF 2884
Ray Lee

This thread was discussed between 16/12/2012 and 20/12/2012

MG TD TF 1500 index

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