What is this thread?

[Chris CooperParticipant @chriscooper5]

I am trying to repair an item which is held together with a bar that has a bit of screw thread at one end. I need to extend this thread a little so as you do you measure up and count threads and apply a thread gauge.

So the bar and the thread are exactly 3/8″ in diameter which leads me to believe that its Imperial and probably BSF.

HOWEVER as far as I can tell (being as the thread is only 1/4″ long) there are 8 teeth in that 1/4 inch which equates to 32 TPI and neither do any of my thread gauges fit it. Its not metric, BA, BSc, BSP, BSW, BSF, UNC or UNF! Just what am I looking at?

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Chris Copper 5, 3/8″ Model Engineer is 32 TPI. Tracy Tools  and Chronos  and others can supply them.

Regards Nick.

[Chris CooperParticipant @chriscooper5]

Agh I never thought of ME threads. The item is not connected to model making or engineering in any way. Thank you.

[noel shelleyParticipant @noelshelley55608]

Nick is right, there is a 32 TPI ME range, so 3/8″ 32 . Noel.

[peak4Participant @peak4]

Just to double check the 32 tpi, as I know I’ve had brain fade in the past.
Is that 8 full threads in ¼” or 8 peaks, which would be a different tpi?

To double check, do you have a 3/16″ BSF tap or die chaser?
Wrong diameter for sure, but it would double up as a 32tpi thread gauge.

Bill

[John PurdyParticipant @johnpurdy78347]

There is also a UNEF (Unified Extra Fine) thread that is 3/8-32 60 degree.

John

[JasonBModerator @jasonb]

As John says several of the American UNEF threads use 32tpi the most common we get in the UK is 1/4×32 for nitro engine glow plugs and small spark plugs as can be seen here .

An idea of where the item may have originated could point to which thread form it is.

[John PurdyParticipant @johnpurdy78347]

Just to make things more confusing my tool catalog lists 3/8 UN taps and dies in 14,18,20,26,27,28,32,36,40,and 56 TPI! So it could be a special!

John

[Robert Atkinson 2Participant @robertatkinson2]

3/8 x 32 UNEF is a very common thread. I have literally thousands of nuts and items with the male thread.
It’s used on electronic components. For example potentiometer mounting bushes and panel mount BNC connectors.

Robert.

 

[vintagengineerParticipant @vintagengineer]

Could be Admiralty Fine.

[Chris CooperParticipant @chriscooper5]

Its on the end of a bar which holds the parts of a chandelier together! I have tried to find out where it originated, but the lady doesn’t know. (I am a volunteer at my local repair cafe, so I see all kinds of things).

[David JuppParticipant @davidjupp51506]

BSB or ‘British Standard Brass’ (which has never been a standard) is the origin of the Model Engineers thread series.  So if the chandelier is old and British, ME could well be possible.

If more recent, or overseas origin, perhaps the UNEF suggestion.

[noel shelleyParticipant @noelshelley55608]

I know the op says it’s 32 tpi but a very common electrical fitting thread is 10mm x1mm, not a huge difference from the 3/8″ 32. In view of what it is I have taps and dies for this very purpose. A mike, a thread gauge and a set of tables are invaluable in cases like this, at least they can get you in the ball park !  Noel.

[JasonBModerator @jasonb]

M10x1 is the standard for new lamp parts, if an older item then it would generally have been 3/8×26 BSB as it was meant for brass tubing

[Chris Cooper 5]

On Chris Cooper 5 Said:

Its on the end of a bar which holds the parts of a chandelier together! I have tried to find out where it originated, but the lady doesn’t know. (I am a volunteer at my local repair cafe, so I see all kinds of things).

Chris,  there are special threads used for the tube used on old style light fittings and used for standard lamps.  They are an “odd ball” size and there is difference between the UK & USA imperial sizes.  I have some info but cannot find it, however here are a couple of links that may be of use.

https://grandbrass.zendesk.com/hc/en-us/articles/203607534-Thread-Size-Chart

What Are the Standard Thread Sizes for Lamps?

Will look in my workshop later and see if I can find anything

John

edit = spelling !

[JasonBModerator @jasonb]

John, I think those are more likely to be found on American items hence why I mentioned the likely source of the part.

IPS or Iron Pipe Standard is more like the current American NPT and for 3/8″ OD which would be 1/8ips the pitch was 27tpi much like NPT today

I’ve seem IPS on some of the old American engine plans too.

[David Jupp]

On David Jupp Said:

BSB or ‘British Standard Brass’ (which has never been a standard) is the origin of the Model Engineers thread series.

Please could you expand on that statement. AIUI, ME threads were standardised by the SMEE around 1912. Does their report/standard/discussion exist? Does it explicitly make the connection to BSB? How strongly do you wish “origin” to be understood?

While there are some similarities  – both BSB and ME are Whitworth form – BSB is strictly constant pitch, whereas ME is not (it uses both 32tpi and 40tpi).

[David JuppParticipant @davidjupp51506]

Everything I’ve read indicates that despite  ‘standard’ in the name, BSB was never an official British Standard.

I don’t have the benefit of access to any SMEE documents.  Perhaps I should have said they have a lot in common, instead of implying which came first.

Maybe you could enlighten us..

[Howard LewisParticipant @howardlewis46836]

I thought that B.S Brass threads (IF there is such a standard), were like Cycle threads, but Whitworth form, and all 26 tpi.

If the thread is Whitworth form and 32 tpi, it is likely to be Model Engineer 3/8 x 32 tpi.

Not knowing the provenance if the chandelier, it could be any thread, but the exact 3/8″ diameter suggests Imperial manufacture, unless made in USA where the thread could be a UNEF

Howard

[Chris CooperParticipant @chriscooper5]

OK, I bought a 3/8 x 32 ME die…..and it doesn’t fit!

I have solved the problem by adding a couple of 3/8 washers to take up the slack.

[Chris Cooper]

On Chris Cooper Said:

OK, I bought a 3/8 x 32 ME die…..and it doesn’t fit!

I have solved the problem by adding a couple of 3/8 washers to take up the slack.

Out of curiosity, maybe use that die to thread a bit of 3/8″ rod and compare the two.

Bill

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