Author Topic: Tap & Die sizes, G 1/8, G 1/4  (Read 1313 times)

Offline pjm01

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Tap & Die sizes, G 1/8, G 1/4
« on: 10.01. 2014 10:42 »
I recently purchased from ALDI a Tap & Die set .... very reasonably priced / good quality etc etc. They are 'millimetre sizes' and clearly not much use for my '59 A7SS, BUT, there are 2 sizes in the kit which baffle me. They are marked (G 1/8 inch, 28 TPI) and t'other (G 1/4 inch, 19 TPI) ..... clearly, they are not either 1/8 and 1/4 inch in diameter but close to 3/8 and 1/2 inch. Any ideas as to what they might be ? Peter M
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Online Brian

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Re: Tap & Die sizes, G 1/8, G 1/4
« Reply #1 on: 10.01. 2014 11:14 »
Peter they are "gas" or "pipe" thread taps. It can all get very confusing as there are lots of different threads that vary from country to country. For instance in the USA NPT (national pipe thread) is 29 tpi instead of the "British" 28 tpi. I dont know how they come up with the diameters as neither are even close to the sizes stated as you have found out.

The world of threads and their forms is a very murky one, lots of different sizes and angles. Even when you have spent a lifetime working with this stuff you still come across odd ones from time to time.
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Offline duTch

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Re: Tap & Die sizes, G 1/8, G 1/4
« Reply #2 on: 10.01. 2014 16:39 »

   'gas' is the same as brass in at least some cases- brass being used for gas as it doesn't spark (in theory at least), but I feel there's fine and coarse depending on the application.

  I also think the plumbing sizing is worked on the 'nominal bore' of the pipe, which would give the ID of the pipe the minor thread diameter- ie not the outside of the tap, but the ID of a die or nut to suit the male thread.......if yea know what I mean..??
....actually....

 A quick  5 second search produced this http://sizes.com/materls/pipeThrd.htm.....only had a quick look, but looks the part
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Online chaterlea25

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Re: Tap & Die sizes, G 1/8, G 1/4
« Reply #3 on: 10.01. 2014 19:47 »
Hi All,
Anything you ever wanted to know about threads on this site

http://www.gewinde-normen.de/en/index.html

Dutch, I have  set of dies marked "brass" they are all 26tpi

HTH
John
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Online Brian

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Re: Tap & Die sizes, G 1/8, G 1/4
« Reply #4 on: 10.01. 2014 21:47 »
Just a quick note purely for information, althought Brass threads are all 26 tpi they are not interchangeable with cycle thread as brass has a 55° thread angle whereas cycle has a 60° angle.
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Online morris

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Re: Tap & Die sizes, G 1/8, G 1/4
« Reply #5 on: 10.01. 2014 22:09 »
And here's another one;

http://www.britishfasteners.com/threads/bsp.html

Helped me out a couple of times... *beer*
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Offline duTch

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Re: Tap & Die sizes, G 1/8, G 1/4
« Reply #6 on: 11.01. 2014 10:21 »
  Thanks John, I knew but got lazy there, and neglected the thread form angle differences, Brass is same as BSF, hey?... but we at A10/7 don't need to deal with that much ;) (gen. sprocket nut, & maybe maggie?- Brass clutch adjuster nuts?)
 
 Just wasn't sure of the Gas as it's obviously different on larger fittings ....I'm no expert though...!
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Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
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Offline Billybream

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Re: Tap & Die sizes, G 1/8, G 1/4
« Reply #7 on: 12.01. 2014 10:15 »
As already advised the threads are British Standard Pipe, but the G = Parallel ( Straight ) thread when British Standard Pipe was more popular as taper thread. Having lived through metrication in the work place, British Standard Pipe threads were adopted as metric many years ago and parallel version used more and more together with sealing washers and spot faces. The other advantage with the G Parallel female thread is male taper threads will still assemble into, thus making drilling/tapping easier.
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Offline pjm01

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Re: Tap & Die sizes, G 1/8, G 1/4
« Reply #8 on: 12.01. 2014 10:24 »
..... and I thought it would be straightforward. Thanks all for your responses. Peter M
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