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Gauge thread?

Posted by em754 
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em754 Avatar
Eric Martin
Jannali, Australia   aus

I am having difficulty getting the knurled nuts that hold the Speedo and Tacho in place on my 67 B, anyone happen to know what the thread would be?
Thanks

Tom Bedenbaugh Avatar
Memphis,Tn, USA   usa
Gerry Avatar
Gerry Masterman
Prairieville, Louisiana, USA   usa

Actually, they're 4BA I think. Close to 10/32 but not exactly. I made some up a few years ago and had to order a special tap to do it. 10/32 nuts got real tight about 1/4" down, indication that the thread pitch is just a hair different. Tried running a 10/32 tap down the threads and was never happy with the resulting thread





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Tom Bedenbaugh Avatar
Memphis,Tn, USA   usa

Never heard of a 4bA thread. I knew that a 10/32 was tight, but just figured the threads were screwed up. I usually just retread the stud, and thumb nut with a 10/32. I guess that my lesson for today.





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Limey Avatar
Eric Marshall
Pentwater, Michigan, USA   usa

According to Mark's Handbook, a 4BA thread has a 0.026" pitch, or about 38 TPI.

BA stands for British Association - and sizes go from 0 to 25 with 0 being the largest! They were very common as small thread sizes in England especially the even sizes 2, 4 , 6 and 8.





Eric and Mary
us-marshalls.net
1974 MGB, 1971 Piper Cherokee, 1971 MGBGT
..... and 1978 Kawasaki KZ650-B2


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Tom Bedenbaugh Avatar
Memphis,Tn, USA   usa

I guess that was a Smith thing. Because all the screw's are 10/32.





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Limey Avatar
Eric Marshall
Pentwater, Michigan, USA   usa

Tom - probably. The threads on SU's were mostly Whitworth and until the mid 70's, almost all the bolts on the exhaust fittings were Whitworth - at least on cars in England!

Interestingly, the thread shapes for both BA and Whitworth have rounded peaks and troughs whereas UN and Metric threads have pointed or squared off peaks and troughs. That makes me think that the old standards were designed for rolled, rather than cut, threads.





Eric and Mary
us-marshalls.net
1974 MGB, 1971 Piper Cherokee, 1971 MGBGT
..... and 1978 Kawasaki KZ650-B2


Member Services:
Headlight relay kits, replacement fuse box kits, headlight alarm, overdrive "reminder", solid state voltage stabilizers and other useful "bits" to help keep your car running at its best.
Steve Carrick
Byron Center, MI, USA   usa

So...

whit and BA are different too? is Whitworth more common to plumbing and BA a screw thread

Barney





Rankin Barnes 74 Sabrina

lbcnut Avatar
James Woolf
NC, USA   usa
1964 MG MGB

Rankin, stuff like TCs, TDs,and TFs have lots and lots of whitworth throughout the car. They also have some BA stuff.


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Limey Avatar
Eric Marshall
Pentwater, Michigan, USA   usa

Yes, Whitworth and BA are different - BA is for smaller diameters. 0BA (the largest) is only 0.236" diameter. The smallest Whitworth thread is 1/4-20.

Whitworth are coarse threads and are almost identical in size and pitch to Unified Coarse threads but, as I stated, the thread shape is different. The biggest problem with Whitworth bolts is the head sizes are very strange - and (I think) directly related to the thread size rather than just an AF (Across the Flats) measurement. Hence the need for Whitworth wrenches.

I am pretty sure that the only Whitworth sizes left on a LBC are on SU carbs - the jet nuts are definitely not sized for AF wrenches.





Eric and Mary
us-marshalls.net
1974 MGB, 1971 Piper Cherokee, 1971 MGBGT
..... and 1978 Kawasaki KZ650-B2


Member Services:
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Ken Lessig Avatar
Nevada, Tx., USA   usa

Eric, I believe there are some Whitworth fasteners in the hydraulics as well, along with the oil pressure gauge hose fittings, at least the original ones.



Post Edited (06-30-05 08:03)



Ken Lessig

lbcnut Avatar
James Woolf
NC, USA   usa
1964 MG MGB

Eric, on the more modern LBCs, like an MGB, MGA, Midget, etc, they have the standard stuff. But on older LBCs, like a T-series, the Y-series, prewar,etc, there is not much of the standard. Most of it is Whitworth and BA.


Limey Avatar
Eric Marshall
Pentwater, Michigan, USA   usa

Ken - yep, I think you are right, I had forgotten about them. Those threads may be BSP (British Standard Pipe) but I'm not certain. Thankfully a decent adjustable will usually work on them, although I think I use a metric wrench on the fitting at the back of the oil pressure gauge!





Eric and Mary
us-marshalls.net
1974 MGB, 1971 Piper Cherokee, 1971 MGBGT
..... and 1978 Kawasaki KZ650-B2


Member Services:
Headlight relay kits, replacement fuse box kits, headlight alarm, overdrive "reminder", solid state voltage stabilizers and other useful "bits" to help keep your car running at its best.
lbcnut Avatar
James Woolf
NC, USA   usa
1964 MG MGB

I think we need to congratulate Eric. He knows more about threads, types of nuts and bolts than anyone I've met before. All this stuff about AF, BA, BSP, Whitworth. It can get confusing but I think he's got it figured out.



Post Edited (06-30-05 08:16)

Limey Avatar
Eric Marshall
Pentwater, Michigan, USA   usa

James - thanks for the accolade, but all I did was look in Mark's Standard Handbook for Mechanical Engineers - sort of the bible for people in my business! However, I do have vivid memories of working on my first car, a 1957 Austin A35, and being completly confused as to why I couldn't find a wrench (spanner) to fit some of the nuts - then I found my Dad's Whitworth set!





Eric and Mary
us-marshalls.net
1974 MGB, 1971 Piper Cherokee, 1971 MGBGT
..... and 1978 Kawasaki KZ650-B2


Member Services:
Headlight relay kits, replacement fuse box kits, headlight alarm, overdrive "reminder", solid state voltage stabilizers and other useful "bits" to help keep your car running at its best.
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