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How to identify an Imperial thread size?


blackrose

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14 hours ago, blackrose said:

Thread is 847/1000" OD (approx), so thread depth is about 112/1000".

I've no idea how to measure the thread pitch but the nut is 508/1000" thick and has 4 threads (I think!) 

You should be able to get an idea if you hold a ruler against the male thread.

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3 hours ago, BEngo said:

Or even BSB (British Standard Brass).  A thread which may be of German origin which actually has no written Standard at all!

N

Whilst there is no written British Standard for the  BSB thread, it certainly has a standard, all BSB diameters are 26 tpi. I have a half set of taps and dies which come in very usefull when restoring old lamps etc. which used BSB for all their fittings before they converted to metric.

 

With regard to the suggested German origin, I would raise several points. Fistly, it's thread form is based upon the British Whitworth thread, secondly why would the Germans invent a thread with imperial measurements, and thirdly why is it called British Standard Brass?

 

 

Edited by David Schweizer
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1 hour ago, David Schweizer said:

 

With regard to the suggested German origin, I would raise several points. Fistly, it't thread form is based upon the British Whitworh thread, secondly why would the Germans invent a thread with imperial measurements, and thirdly why is it called British Standard Brass?

Machinery's guide to world screw threads notes only that the origin is obscure, but may be the result of an early attempt at standardisation by the makers of gas burners, and that there is an identical series in a range of diameters in Germany.   I guess you  will know more than me about the possibility of early German gas burner makers joining in or getting into the market early enough to be standard setters.

 

I do not suggest a German origin for the thread form, only the possibility that the fixed pitch series known as BSB was defined there.  We have Mr Whitworth to thank for the thread form  What is now the BS Whitworth thread form was the first thread form to be standardised  so it is not unlikely that it would be used outside the UK.  It still pops up in use in some odd places these days. I have seen it in Italian made washing machines and in AC generators as well as some far eastern stuff.   It is a good thread for aluminium alloy and cast iron.  It is usually slightly coarser than a similar sized metric coarse thread so still has utility where the coarsest standard thread is needed.  

.

N

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8 hours ago, bizzard said:

And there's BS Bicycle thread, tall and very fine threads for a good grip so the wheels don't fall off. .  As for BS Lawnmower threads. :)

Also Raleigh bike thread is finer, 22 tpi than BS bike thread. No help to the OP though.

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21 minutes ago, Tacet said:

Isn't cycle thread 26 tpi?

I am in error, you are correct, mostly

 

BS bike is 26 tpi but most bottom brackets are 24 tpi except many Raleigh which are 26 tpi.  Why I put 22 is odd, its my age.

There is a 25.5 tpi metric thread which causes confusion on bikes imported from Europe but not China which uses 26 tpi.

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31 minutes ago, Tracy D'arth said:

I am in error, you are correct, mostly

 

BS bike is 26 tpi but most bottom brackets are 24 tpi except many Raleigh which are 26 tpi.  Why I put 22 is odd, its my age.

There is a 25.5 tpi metric thread which causes confusion on bikes imported from Europe but not China which uses 26 tpi.

Also, from recollection, Carlton.  And I mean proper Carltons before they were taken over by Raleigh.

6 hours ago, BEngo said:

Machinery's guide to world screw threads notes only that the origin is obscure, but may be the result of an early attempt at standardisation by the makers of gas burners, and that there is an identical series in a range of diameters in Germany.   I guess you  will know more than me about the possibility of early German gas burner makers joining in or getting into the market early enough to be standard setters.

 

I do not suggest a German origin for the thread form, only the possibility that the fixed pitch series known as BSB was defined there.  We have Mr Whitworth to thank for the thread form  What is now the BS Whitworth thread form was the first thread form to be standardised  so it is not unlikely that it would be used outside the UK.  It still pops up in use in some odd places these days. I have seen it in Italian made washing machines and in AC generators as well as some far eastern stuff.   It is a good thread for aluminium alloy and cast iron.  It is usually slightly coarser than a similar sized metric coarse thread so still has utility where the coarsest standard thread is needed.  

.

N

No, I actually know nothing about German gas burners, but as the British Gas Burner industry was probably the biggest in Europe, I doubt that German burners were ever imported. As a matter of interest all the Gas light burners I have worked on used BSB threads.

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17 hours ago, Richard T said:

Sadly he retired and no one would take on the business. Charnwood fasteners have moved down to near B&Q.

Ah, that's a shame. Ten years since I lived there, so not a supprise it's changed. What about the Landrover guy, or West End Motors?

 

I had call for an M7 tap once, not expecting much joy I went in to ask if he had one or could get one.

He opened the wooden case in is hands, pulled out the tap sitting on the divider between M6 and M8, asked what my intended use was as, and then said 'this one is for cast iron, but it should do you fine. It did, and the kitcar still uses the spindle adapter it (and the uni workshop lathes) made to this day.

 

Daniel

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The pitch of the old German DIN standard thread for steel electric conduits (Stahlpanzerrohrgewinde, abbreviated as  PG) was defined in terms of "threads per english inch". In principle, its use in Germany was discontinued in 2001 in favour of metric conduit, however some PG fittings, such as cable glands, still seem to be widely available, even in the UK. PG has a 80° flank angle, and is a surprising omission from my copy of  Machinery's  "Guide to World Screw Threads" book (1970  edition). I guess it was established before metric threads became standardised by international agreements in the late Victorian era. Unlike ordinary nuts and bolts, new pipes often have to joined to old pipes. There is little point in changing for change's sake, so BSP with its Whitworth thread form remains the world standard for general purpose screwed iron pipes (other than in North America).

Another way of establishing the type of internal thread is to screw a piece of wood into the bore. It doesn't need to be perfectly circular, just small enough so that the highest parts are scored by the thread. However, as Whitworth and UNC have identical pitches in the size range of interest, wax, gum, or Plasicene  would be needed to make an accurate impresion of the thread form to distinguish 55° Whitworth from 60° UNC. 

Edited by Ronaldo47
Typos
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