Need Help Identifying Tap & Die Size

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Yak18pilot
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Need Help Identifying Tap & Die Size

Post by Yak18pilot »

The mounting for the scale whistle on my live steamer needs to have the threads chased, but I'm having a hard time identifying what size tap & die to obtain. By comparing the threads with other taps I have I've determined that it is 40 TPI, but don't know the size. I've attached some photos of the dimensions. Hopefully someone can identify what size this is.
Thanks in advance!
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Carrdo
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Re: Need Help Identifying Tap & Die Size

Post by Carrdo »

1/4-40 ME (model engineer) is my best guess.
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milwiron
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Re: Need Help Identifying Tap & Die Size

Post by milwiron »

Is the thread tapered? With the end tilted towards the camera the thread looks straight or parallel. If it's tapered it would be a 1/4-40 Model Taper Pipe or MTP.

Less likely-
There's also a UNS Unified National Special or UST Universal Straight or Tapered which I believe will fit the others.
Denny
Last edited by milwiron on Mon Jun 28, 2021 2:07 pm, edited 1 time in total.
"Measure twice, curse once."
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cbrew
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Re: Need Help Identifying Tap & Die Size

Post by cbrew »

here is a source
https://www.pmmodelengines.com/shop/too ... taps-dies/
from the pictures, it appears to be straight cut threads.
If it is not live steam. its not worth it.
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Dick_Morris
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Re: Need Help Identifying Tap & Die Size

Post by Dick_Morris »

The whistle and elbow commercial fittings are probably MTP. If so, it would be logical for the builder to follow suite with other threads on the piping.
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gwrdriver
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Re: Need Help Identifying Tap & Die Size

Post by gwrdriver »

With a cast elbow my initial thought would be that it's MTP, but I don't see a definite taper on the thread, so I would then think 1/4-ME.

But something else bothers me about the installation. As I see it, it's mounted in a very precarious position where if accidentally bumped or tugged on when in steam, the pipe connection could be broken by the pipe acting as a lever. If it were mine I would shorten both pipes, especially the horizontal one, so as to reduce the potential for accidental breakage.
Perhaps a dome cover we don't see protects the pipes as well as prevents shortening.
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Yak18pilot
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Re: Need Help Identifying Tap & Die Size

Post by Yak18pilot »

Thanks for the help!
There's a steam dome cover that I have removed to gain access to the safety valves so the pipe for the whistle is protected for most of its length
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Bill Shields
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Re: Need Help Identifying Tap & Die Size

Post by Bill Shields »

with GWR on this...accident looking for a place to happen....heck, just pulling on the whistle lanyard could snap it off...
Too many things going on to bother listing them.
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