Help please. 1 1/2" diameter thread identification

[Eyefor]

Hi.

Would anyone know how to identify the thread size in the picture which shows the top of an old mahogany theodolite tripod that I would like to use as a standard lamp and, rather than drilling the original (threaded) brass cap, I would like to create an adaptor in order to screw a lamp holder onto the male thread so the tripod isn't irrevocably damaged.

The thread is 1 1/2" outside diameter so maybe 1 1/2" bsp?

Thanks in advance.

 

[London Best]

If the thread measures 1 1/2 inches outside it is definitely NOT 1 1/2 BSP as BSP threads are quoted by the nominal inside diameter of the pipe.

[Mice!]

7 minutes ago, Eyefor said:

The thread is 1 1/2" outside diameter so maybe 1 1/2" bsp?

It could be a B.S.F or Whitworth thread if it measures 1.5, a BSP Would measure 1.882 (sorry)

Any machine shops near you so you can find out the TPI?

The Whitworth is 6tpi and the BSF is 8, your thread doesn't look course enough for that so could easily be metric. 

[mellors]

27 minutes ago, Eyefor said:

Hi.

Would anyone know how to identify the thread size in the picture which shows the top of an old mahogany theodolite tripod that I would like to use as a standard lamp and, rather than drilling the original (threaded) brass cap, I would like to create an adaptor in order to screw a lamp holder onto the male thread so the tripod isn't irrevocably damaged.

The thread is 1 1/2" outside diameter so maybe 1 1/2" bsp?

Thanks in advance.

 

I would take it and try local plumbers merchant /screwfix looks very similar to the old iron/brass fittings used on threaded pipe. 

Also try plastic waste fittings 

Edited September 15, 2023 by mellors
Extra info

[Rupert]

Go to a nut and bolt place and ask for a nut to fit this.

[Eyefor]

18 minutes ago, Mice! said:

It could be a B.S.F or Whitworth thread if it measures 1.5, a BSP Would measure 1.882 (sorry)

Any machine shops near you so you can find out the TPI?

The Whitworth is 6tpi and the BSF is 8, your thread doesn't look course enough for that so could easily be metric. 

It's over 100 years old so not likely to me metric?

12 minutes ago, mellors said:

I would take it and try local plumbers merchant /screwfix looks very similar to the old iron/brass fittings used on threaded pipe. 

That is what I was thinking - just trying to avoid walking into screwfix, tripod under arm, and asking "can you tell me what this is please"?  🤔

1 minute ago, Rupert said:

Go to a nut and bolt place and ask for a nut to fit this.

Yes, but same issue as above with Screwfix - but may be the only option. 

[amateur]

Alternatively, invest in some screw pitch gauges - less than £6 on the Bay

[Mice!]

15 minutes ago, Eyefor said:

It's over 100 years old so not likely to me metric

Probably a Whitworth then.

10 minutes ago, amateur said:

Alternatively, invest in some screw pitch gauges - less than £6 on the Bay

That's the way to go,  find out the tpi and thread angle,  probably 55°

[Eyefor]

10 minutes ago, amateur said:

Alternatively, invest in some screw pitch gauges - less than £6 on the Bay

Almost as long ago as this item is old, I was a toolmaker. Somewhere I have my screw pitch gauges and pocket charts. Not seen either in years!

[Mice!]

4 minutes ago, Eyefor said:

Almost as long ago as this item is old, I was a toolmaker. Somewhere I have my screw pitch gauges and pocket charts. Not seen either in years!

But you thought it was 1.5 BSP 😯😉

[Eyefor]

20 minutes ago, Mice! said:

But you thought it was 1.5 BSP 😯😉

 

To me the pitch just looks too wide for whit.

Off to plumbers merchants...

[Yellow Bear]

BSP would be 1.3 or 1.7 inches

[Stimo22]

If it is that old it could be a special thread to that company,  Many company’s did this. Attached is a chart of the various threads per inch. There is also a Brass thread that the railway used a lot and is 26 tpi.  You need to use a tpi gauge to measure, you can’t be far from me near Milton Keynes if you need it measured

Edited September 15, 2023 by Stimo22

[amateur]

1 hour ago, Eyefor said:

Almost as long ago as this item is old, I was a toolmaker. Somewhere I have my screw pitch gauges and pocket charts. Not seen either in years!

In that case, you would have the skills and knowledge to stick a rule or a pair of calipers on the thread and get an accurate count, rather than asking this bunch of randoms 🤣

[Mice!]

27 minutes ago, amateur said:

In that case, you would have the skills and knowledge to stick a rule or a pair of calipers on the thread and get an accurate count, rather than asking this bunch of randoms 🤣

His calipers are with his pitch gauges 😄😄

[Eyefor]

29 minutes ago, amateur said:

In that case, you would have the skills and knowledge to stick a rule or a pair of calipers on the thread and get an accurate count, rather than asking this bunch of randoms 🤣

Sitting on a pile of rubble awaiting plumbers who would "definitely be here by 10am" (today), I don't have access to calipers or anything to get an accurate measure - but I do have access off my laptop to this "bunch of randoms" (bit harsh? 😉) and a tape measure of the threaded collar (close enough to 1/2") gives me more than 6 tpi for whit. 

1 minute ago, Mice! said:

His calipers are with his pitch gauges 😄😄

True. And in my reloading kit.

Edited September 15, 2023 by Eyefor

[Eyefor]

34 minutes ago, Stimo22 said:

If it is that old it could be a special thread to that company,  Many company’s did this. Attached is a chart of the various threads per inch. There is also a Brass thread that the railway used a lot and is 26 tpi.  You need to use a tpi gauge to measure, you can’t be far from me near Milton Keynes if you need it measured

Thanks. If I get stuck I'll let you know but I should be able to find my pitch gauges if they are where I think they are.

[RCB56]

Definitely NOT Whitworth. My guess looking at the picture is 1" BSP at 11 tpi and     1.3 " dia. or

1 1/4" BSP is 11 tpi and 1.6 dia.

[derbyduck]

it looks like it is 1 1/4 british standard gas ,same size as bsp but a parallel thread . a bsp socket will fit on it

Edited September 15, 2023 by derbyduck

[cash1]

"same size as bsp but a parallel thread" BSPP? It also depends how old the theodolite tripod is. Pre Whitworth threads were all over the place especially in the USA.

Any engineering workshop would tell you what it is free of charge. 

I reckon I'm getting old I've got a ZEUS book that cost 2/6p

[wyn]

I have a tripod here that measures about 2" by 13 tpi.   Apparently every manufacturer up to 1909 used their own threads.

 

 

[Mice!]

On 17/09/2023 at 14:08, wyn said:

I have a tripod here that measures about 2" by 13 tpi.   Apparently every manufacturer up to 1909 used their own threads.

 

 

I guess they could do when it was just for parts made in house, 2" by 13 tpi is definitely made up.

@Eyefor did you ever find out what the thread was?

[Andy H]

13 Tpi is almighty close to 2mm thread pitch , Could it be a 38 x 2mm thread .https://www.amazon.co.uk/Burkit-Metric-Threading-Machine-Thread/dp/B0B5DFN7W8

 

Edited September 25, 2023 by Andy H

[manton]

Unless you can find something with this thread you will need to get someone to screw cut it on a lathe as a tap of this size would cost a fortune .

[Eyefor]

On 17/09/2023 at 14:08, wyn said:

I have a tripod here that measures about 2" by 13 tpi.   Apparently every manufacturer up to 1909 used their own threads.

 

 

 

19 hours ago, Mice! said:

I guess they could do when it was just for parts made in house, 2" by 13 tpi is definitely made up.

@Eyefor did you ever find out what the thread was?

 

9 hours ago, Andy H said:

13 Tpi is almighty close to 2mm thread pitch , Could it be a 38 x 2mm thread .https://www.amazon.co.uk/Burkit-Metric-Threading-Machine-Thread/dp/B0B5DFN7W8

 

Thanks for all replies and my apologies for the delay in reply but we have been away.

Found my old thread gauge and it is 13 TPI so I might try the 38 x 2 as that might work.