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Need help on Thread call-out/designation on drawings

HaroldL

Alibre Super User
I looking at some old drawings from the Carreras Soto collection on STUDYCAM BLOGSPOT that have some thread callouts that I am not familiar with. In the attached image does anyone have a clue what the circled callouts are and where can I get some docs or charts that specify the parameters of the thread?
I am guessing that the "W16" could be a Whitworth thread but nothing I have found on Whitworth appears to be anything like on the drawing. And I have no idea what the "Rg" is. It looks like the diameter is given but not the thread pitch. Could that be a pipe thread?

TIA for any help.

Carreras soto 14_4.png
 

Ken226

Alibre Super User
I'm not familiar with those callouts.

I'm a member of Hobby Machinist forum. There are some knowledgeable folks over there when it comes to non standard thread specs. I can try and post your pic and see if anyone knows?
 
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Ken226

Alibre Super User
Not sure about the top one. My best guess would be a Whitworth.

The bottom one could be a British standard pipe thread?

-12, 3/4 14tpi, OD 26.4mm

The middle one, -08 1/2 14tpi. 20.9mm OD. (Not exact but close).
 

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idslk

Alibre Super User
Hello Harold,

Rg should identify conical threads (G only, is for cylindrical threads...as far as i remember)
Maybe this SITE is interesting for you.

Regards
Stefan
 

DavidJ

Administrator
Staff member
Harold the 2 'Rg' thread sizes given are very close matches for BSP threads - most (but not all) references indicate that the R is for tapered thread (so not a single diameter anyway - just a nominal) . The W is fairly close to a BSP size but I suspect is a special having Whitworth thread form (same as in the BSP threads) for for whatever reason a non-standard diameter was chosen - so 16mm diameter x 19 TPI. It only seems to be there to allow the whistle dome position to be adjusted.

As the drawing shows a whistle driven by steam or air - pipe threads make sense for the connections.

This is one of the clearer references I found to explain G/R etc. but doesn't give full detail for dimensions
 
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HaroldL

Alibre Super User
Guys, thanks for the info and links, they help to clear the fog. All my work in the past had either Metric or Unified thread so these designations puzzled me.
 
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