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Mystery thread

PostPosted: 13 Oct 2021, 17:21
by Guineafowl21
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?

Re: Mystery thread

PostPosted: 13 Oct 2021, 17:44
by Trevanion

Re: Mystery thread

PostPosted: 13 Oct 2021, 17:47
by Woodster

Re: Mystery thread

PostPosted: 13 Oct 2021, 18:55
by Guineafowl21
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.

Re: Mystery thread

PostPosted: 13 Oct 2021, 19:49
by 9fingers
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

Re: Mystery thread

PostPosted: 16 Oct 2021, 19:03
by Guineafowl21
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.

Re: Mystery thread

PostPosted: 16 Oct 2021, 20:11
by 9fingers
Result!

Bob