Gauge thread?

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

10/32

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

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.

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.

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

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.

So...

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

Barney

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

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, 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)

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.

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!

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)

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!

I wish I could find a Whitworth set around here......

Moss has 'em - <http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=31567>

Here's a supplier for the obsolutete Brit stuff <http://www.britishtool.com/socket.htm>
It is where I bought my 4BA dies and taps

Personally, I want to run as fast as I can from anything that has Whitworth fasteners involved. It's bad enough having to jump from fractional sizes to metric. Had a bunch of old Triumph bikes that were full of WW stuff years ago and it was a PITA

Here's another one for British tools. Also supporters of the LBC hobby in general, which makes them OK in my book:

<http://www.britishfasteners.com>

Thanks very much for all your help.........looks like i will have to find myself a 4BA tap to make my own, much appreciated.

James,

http://www.rabers.com/parts/tools/ $50

I have used cheap wrenches and filed them to whit. size

I know Moss sells Whitworth stuff. It's just so expensive. Like all tools. I'm watching a couple of sets on eBay right now. Might throw a bid in on one of em. I don't need a brand new set. Just something reasonable and useable. I've bought most of my other good tools new so I guess I am allowed to skimp here and buy some quality used ones.

If I just had to have wrenches to fit Whitworth I'd buy a set of cheap open end wrenches and grind/sand the openings to fit. A belt sander works great for thei. I have done the same thing to make special wrenches for the odball oil cooler hose nuts and odd sized bolts/nut on guns that I used to work on. Afterward, I paint the wrenches with yellor paint to show that they are specially modded tools when they end up in my toolbox