Help identifying a mystery thread

[Beardy MikeParticipant @beardymike]

I recently had something of an unscheduled stop with my Juliet; I seem to have escaped almost unscathed, apart from my displacement lubricator that took a bit of a bash. I need to replace the adjuster shaft, which has clearly been made from a piece of studding.

Based on everything else being imperial, I took a rough od measurement and ordered the closest BA size to what my calipers suggested (7BA). Unfortunately this doesn’t fit. It’s rather fiddly to see exactly what I’m doing, but as far as I can tell the pitch is slightly coarser than 7BA, but the od slightly smaller. I’m a little sceptical of diameter measurements as the thread crests look a bit mashed. It’s definitely not 6BA as I’ve got some of those on hand to compare to.

Other components all seem to be BA or ME threads, but in desperation I did try m2.5, unc2 and unc4 which I had on hand without any luck.

Does anyone have any idea what this thread might be? I’d prefer to find the right studding than resorting to tapping up a size as most of my taps are metric.

Thanks,

Mike

[BazParticipant @baz89810]

Nearest to 7BA but coarser could be 3/32 Whit.

[Howard LewisParticipant @howardlewis46836]

Not knowing the locomotive, nor this particular one, my guess would be 3/32 BSW. Unless made in USA, and being a “vintage” design, t

Check the pitch of the thread (AND if you have thread gauges) the form.

Whit form (BSW, BSF, ME, BSP and Brass, will be 55 degrees. Unified or Metric threads will be 60 degree.

3/32 BSW will be 48 tpi

A lot of questions of this sort can be answered by buying a set of Zeus Charts, and the Model Engineers Handbook by “Tubal Cain” (The British one, not the North American using the same name) You can refer to them at any time, and gain a lot of useful knowledge.

Howard

[Beardy MikeParticipant @beardymike]

I’ve got thread gauges; what I pack is eyesight good enough to get a confident reading, especially on damaged threads…

I also wanted to see if anyone suggested another thread series I didn’t know about – unless I knew BA threads existed I’d have been very confused by their non-round-number tpi for example.

I’m going to take it into work and use some magnification/measuring kit in the lab to see if I can get a better measure of it. I’ll see if it matches 3/32BSW to a sensible tolerance.

Thanks,

Mike

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Beardy Mike, below is all I can find about Juliet’s displacement lubricator.

Regards Nick.

[Beardy MikeParticipant @beardymike]

Wow, that’s excellent – looks a lot like what my loco has, although with a few tweaks. I take it that the 3/32 without a thread form stated should be taken to be bsw?

Thanks,

Mike

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Mike, seems like bsw is the only one that is standard for 3/32″ and perhaps that is why the thread form isn’t stated on the drawing, but I would still check the one you have, in case the builder choose something else.

Regards Nick.

[DalboyParticipant @dalboy]

Has the original builder mixed threads and used an American thread 5-44. Just a crazy thought from me

[Dalboy]

1. On Dalboy Said:

   Has the original builder mixed threads and used an American thread 5-44. Just a crazy thought from me

   That is entirely possible  i have been known to use mixtures of British and American threads, and even Metric, depending on what taps and dies I have available in my workshop. I seem to have all sorts of incomplete sets acquired over the years, plus various ones lost or broken. I’m sure I’m not the only one so afflicted.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, Mike has said that 7 BA was no good, and the measurement he got  of the one he has is smaller in diameter, so a 5-44 would be too big, 7 BA O/D is 0.0984″,  5-44 OD is 0.1050″.

Regards Nick.

[Beardy MikeParticipant @beardymike]

I got it under some magnification and found that it’s a good match for 48tpi. I’ve ordered the whitworth die.

Thanks for the help folks. I’m crossing my fingers that it’ll be a pretty trivial fix once the die turns up

[Nicholas Farr]

On Nicholas Farr Said:

Hi, Mike has said that 7 BA was no good, and the measurement he got  of the one he has is smaller in diameter, so a 5-44 would be too big, 7 BA O/D is 0.0984″,  5-44 OD is 0.1050″.

Regards Nick.

I read the post as somewhere between 7BA and 6BA that is why I went for that measurement

[Neil AParticipant @neila]

If the builder followed the instructions on the ME pages above, then the thread is most probably 3/32 Whitworth.

The clue is the No 48 drilled hole which is then tapped 3/32. The No 48 is the pre-metric tapping size for 3/32 Whitworth.

There is always a little uncertainty in what a previous builder used, it depends on the age of the build and what the builder had to hand at the time. I tend to use metric threads now, but that does not stop me using Whitworth if I think it appropriate.

Neil

[John PurdyParticipant @johnpurdy78347]

Nick

I believe #5 UN is .125″OD (finger trouble?).

John

[Nicholas FarrParticipant @nicholasfarr14254]

Hi John, thanks for pointing that out, I don’t know why the 0 slipped in instead of a 2, so yes it should be 5-44 OD is 0.1250″.

Regards Nick.

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