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Mystery thread

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Mystery thread

Postby Guineafowl21 » 13 Oct 2021, 17:21

I’ve been asked to repair one or two of these wingbolts, fitted to the tripod legs of a wartime trench periscope/telescope:

image.jpg
(289.23 KiB)


A couple have snapped off at the recessed portion.

The thread diameter is 0.245”, and it’s 30 TPI, which my lathe can’t do. Any ideas what the thread might be so I can get the right die?
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Re: Mystery thread

Postby Trevanion » 13 Oct 2021, 17:44

"A machine can only be no better than the man who works it. His is the intelligence, the machine has none." Sydney Lister, 1949
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Re: Mystery thread

Postby Woodster » 13 Oct 2021, 17:47

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Re: Mystery thread

Postby Guineafowl21 » 13 Oct 2021, 18:55

Thanks - that looks like it, but I wondered what the thread was. I’ve seen a reference to UNS, but the thread charts I found don’t mention it.
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Re: Mystery thread

Postby 9fingers » 13 Oct 2021, 19:49

Guineafowl21 wrote:Thanks - that looks like it, but I wondered what the thread was. I’ve seen a reference to UNS, but the thread charts I found don’t mention it.



Unified Special will have a 60 degree thread angle which from the age/origin is unlikely.
Yours will most likely be 55 degree whitworth form.

Bob
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Re: Mystery thread

Postby Guineafowl21 » 16 Oct 2021, 19:03

9fingers wrote:
Guineafowl21 wrote:Thanks - that looks like it, but I wondered what the thread was. I’ve seen a reference to UNS, but the thread charts I found don’t mention it.



Unified Special will have a 60 degree thread angle which from the age/origin is unlikely.
Yours will most likely be 55 degree whitworth form.

Bob

Thanks - I found an old die on ebay, sold as 1/4”x30 Whitworth form, and it worked perfectly.
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Re: Mystery thread

Postby 9fingers » 16 Oct 2021, 20:11

Result!

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