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Discussion Starter #1
Getting away from cockroaches, human rights and the Election for a few minutes, can I pick some engineering brains out there…

I have a couple of electrical terminal posts here for which I’m looking for nuts. Terminal post are essentially threaded rods about an inch and a half long, these can be put through suitably sized holes in the side of a box. A couple of nuts, one on either side secure them in place. Wires can then be twisted around both ends of the threaded rods or soldered onto suitable solder tags and secured in place with a second nut. This allows electrical contact to be made between the inside of the box and the world outside. The nuts on the outside are quite large and covered in plastic so they can be tightened/loosened by hand. These terminal posts would normally be used in non-conductive boxes i.e. plastic otherwise they would obviously short. For use in metal boxes an insulating sleeve went over the rod.

My apologies to those who are already familiar with terminal posts…

Now I have mislaid the nuts and am looking ‘everywhere’ for replacements, without luck. Everybody has metric screws/nuts and I suspect these date back to pre-metric days, I don't even know whether they were made in the UK or not.

Similar electrical terminal posts are easily obtained cheap on eBay but they are usually 4mm and are a bit too small.

The threaded rod measures 6mm on my cheap Chinese digital callipers, bought recently for under £6 at a local boot sale – how can they make them for that price – and ship them over here? I have tried to count how many threads per inch and reckon it’s ~28 or 29.

I’ve been looking at a chart here which should probably help:-

http://mdmetric.com/tech/tic1c.htm

but all it does is confuse…

From the meagre information I’ve given I wonder can anyone possibly identify these?

Looking at the chart I thought maybe it’s a BA but that should have 25.4 threads per inch if I read the chart correctly.

Give me electronics any time – it’s so much simpler !!!
 

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I got stumped by a thread form once and it turned out to be JIC
( Joint Industrial Council ) common in Japan.
Usually a flare type fitting but not always. JIC thread charts are on the Net.
 

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1 B.A. = 28.25 T.P.I. so if you've counted the threads as between 28 & 29 then that should be the one.

Ron.

edit: your 6mm measure for the O.D. of the rod sounds about right. 6mm = 0.2362 inches. The O.D of the threaded portion should be 0.2087 inches.
 

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Are you sure they're not Unified screw threads below 1/4" the standard attachment thread used in electronics and electrical work. Try looking at a set of Zeus tables.
 

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On older electrical connections BA is always a good assumption, to start anyway.

I can recall that as recently as the 1960s some larger manufacturers devised and used their own threads for their own equipment - The idea, so I was told, was to discourage people using other companies kit on a single contract. Thus MK would not fit Crabtree would not fit Reyrolle etc etc.
 

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Whilst on the subject of threads.

Bought a thread gauge Imp/Metric. found one Imp was 19.5 tpi.

Does anybody know what its used for? Been a grey cell twister for 2 years.
 

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Spongebob
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BA thread form was a British standard for the electrical industry years ago.
I still have a full set of BA taps and dies that belonged to my father but they have not seen the light of day for many a year.
Remember the BSA thread for bicycles?

Bob
 

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Whilst on the subject of threads.

Bought a thread gauge Imp/Metric. found one Imp was 19.5 tpi.

Does anybody know what its used for? Been a grey cell twister for 2 years.
Hi Pampas.
The only thread I can find with 19,5 t.p.i. is the “Lowenherz” (Lionheart) thread.
It is based on the metric system and was (maybe still is) used on fine threads for measuring instruments, optical apparatus etc., especially in Germany.
It is a 9mm. thread with a pitch of 1,3mm.
Ref:- Machinery's Handbook, 12th.Edition 1815 pages, published 1943.

Regards Ron.
 

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Discussion Starter #11
Thanks for the info guys.

Zero – I’ve looked at UNC, UNF & UNEF and I can’t see anything that appears to fit.

I’ve checked again and I’m pretty sure the thread diameter is near as dammit 6mm whilst pitch is ~28 per inch.

Ron – your suggestion of it being a 1BA sounds good.

The one thing that confuses me a bit is that 0 BA is ~6 mm (0.023) but that has a pitch of 25.4 tpi whilst this definitely has nearer 28, so on balance a 1 BA?

Thanks again for your suggestions.
 

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It is almost certainly a BA size if it is from electrical equipment manufactured before the early 1970s. Most ships electricians at that time could identify the BA threads just by looking at them as they were very common.
I tried to attach a table from the 1953 edition of the naval electrical pocket book which gives dimensions of the various BA sizes in inches and will copy them here.

Number Threads per inch Diameter major Minor Drill tapping No clearance no

0BA 25.4 0.2362 0.1890 12 B
1BA 28.2 0.2087 0.1661 19 3
2BA 31.3 0.1850 0.1458 26 12
3BA 34.8 0.1614 0.1269 30 19

It goes on up to 10 BA
It also has information n dimensions for drills , and whitworth and BSF screw threads.
I can not attach here but if you want me to try to copy it and send by e mail send me a private message with an e mail address
 

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Unfortunately I tried to copy the dimensions as a table but it did not work however if you use the headings above the numbers and separate the numbers it should work. example
Number 0BA Threads per inch25.4 Diameter major 0.2362 Diameter minor 0.1890 drill tapping no 12 clearance no B
 

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Hi Johnvvc. You have set an interesting conundrum with this request. You state the O/D as 6mm or 0.236" and the pitch as 28TPI approx. I have checked for 28 TPI on all the thread forms I know of. Have you used thread gauges to determine the pitch? The threads I have found are as follows. American NF No12 & 1/4", BSF 7/32"(0.2187"), BSP 1/8" (0.383"), UNExF. 7/16"&1/2",UNF No12 & 1/4", UNF(28un series) starts @ 5/16", 1BA is almost 28TPI, 6mm is 1.0mm, If you divide 25.4mm X 28 it is 0.91mm getting close as an approx. So if you can't get anything to fit, run a 6mm X 1.0 die down the posts as metric is very easy to obtain.
Bill
 

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Hi Johnvvc. You have set an interesting conundrum with this request. You state the O/D as 6mm or 0.236" and the pitch as 28TPI approx. I have checked for 28 TPI on all the thread forms I know of. Have you used thread gauges to determine the pitch? The threads I have found are as follows. American NF No12 & 1/4", BSF 7/32"(0.2187"), BSP 1/8" (0.383"), UNExF. 7/16"&1/2",UNF No12 & 1/4", UNF(28un series) starts @ 5/16", 1BA is almost 28TPI, 6mm is 1.0mm, If you divide 25.4mm X 28 it is 0.91mm getting close as an approx. So if you can't get anything to fit, run a 6mm X 1.0 die down the posts as metric is very easy to obtain.
Bill
Bill,
I really wouldn't recommend trying to rethread the terminal post as after the first 3 or 4 threads have been re-cut the die will begin cutting off the tops of the succeeding threads.
As spongebob & forthbridge have said, the BA was the standard for the electrical industry & from my experience, posts for mounting PCB's (but I am going back some 50+ years) were almost always to BA standard.
johnvvc,
If you really can't get hold of 1BA nuts, you could use 6mm x 1mm pitch nuts, running a tap down the nut & leaning the tap slightly (as you rotate) to cut an oversize thread. Otherwise if you can get hold of a 1BA tap, just retap the 6mm x 1mm nut with it.

Ron.
 

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Discussion Starter #16
Thanks again for your suggestions.

As there seems good ground for thinking this may be 1BA I’ve ordered some nuts – if they won’t fit they’ll be consigned to the garage with all my other bits and pieces – no great problem.

I’ve checked my measurements again this morning.

I had suspected the jaws of my expensive callipers (£5 or £6 at the local boot sale…) might not be parallel but today I notice that as they are very ‘narrow’ at the end furthest from the body there is a tendency for them to actually go partly inside the thread and give a slightly lower reading. I have been measuring this way and getting a reading of 6mm – 0.23”. Now further in the jaws are wider and measuring here gives me 6.2mm – 0.24”.

The above description of the calliper jaws may be a bit misleading… Imagine looking at the jaws end on – at the extreme end of the jaws they almost resemble a pair of blunt knife blades so the two coming together would go partly into the thread and not be measuring it’s outside diameter.

As for measuring the TPI, I have been doing thus under a magnified lamp and am pretty sure that the figure of 28 is about right – plus or minus a very small amount.

We’ll see what happens when the 1BA nuts arrive next week.

Thanks again for your interest and suggestions.
 

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The above description of the calliper jaws may be a bit misleading… Imagine looking at the jaws end on – at the extreme end of the jaws they almost resemble a pair of blunt knife blades so the two coming together would go partly into the thread and not be measuring it’s outside diameter.
What prevents you from measuring the O/D of the thread 'end-on' to the screw, rather than across it? That way the calliper jaws can't go anywhere but on top of the threads. Just a suggestion.
 

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Discussion Starter #18
What prevents you from measuring the O/D of the thread 'end-on' to the screw, rather than across it? That way the calliper jaws can't go anywhere but on top of the threads. Just a suggestion.
and a good one...

I did think of that earlier but somehow couldn't get the caliper and the screw at the same level, tried it again and it confirms the diameter is 6.2mm.

Thanks Ron.
 

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Hi Johnvvc once again. This thread (no pun) is getting more and more interesting. Being a battery terminal of some age, it would be natural to assume the threads are B.A. I found a table for B.A. threads in an old book and it is interesting to note, 0BA and 6mm x 1.0 pitch are identical except for the thread angle. Therefore a M6 nut will fit on an 0BA thread but not the reverse.
Will post book table.
Bill
 

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