OT: mystery tap: Dalzen 0.820 OD x 8tpi bottoming tap, LH threads, sine wave tooth shape, HSS, 4 flute

[JHarveyB]

I have a mystery tap (acquired long ago in a heap of things at a sewing machine factory out-of-business auction) that I need help identifying and finding a new home for. Inscribed on the shank are: Dalzen; 0.820-8 LH; T-60; HSS. It is a bottoming tap (no taper to the initial cutting area). The teeth are a sine wave shape, i.e., rounded tips and gullets. I would like help identifying the thread type and nominal size. If anyone here could use this tap, I would be willing to mail it to you for shipping plus whatever you wish to pay me for it. Otherwise I will probably try my luck on eBay (less desirable option). Thanks for your help!
JHarveyB

 

[eKretz]

Knuckle thread. Couldn't tell you the application though.

 

[DDoug]

That thread form (or very similar) is used on concrete forms, the dried concrete splits off easily.
But not that fine of pitch, nor Left hand:

McMaster-Carr

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[kenton]

Knuckle thread - Wikipedia

en.wikipedia.org

To save the time searching.

 

[4GSR]

Forum member M.B. Naegle maybe interested in that tap since it came out of a sewing machine factory.
Ken

 

[JHarveyB]

Thanks for your help. I checked with M. B. Naegle and he is unfamiliar with that thread. Still looking for someone who can use it.

 

[wheels17]

here are a lot of really odd taps loose in the world. Anybody need a 2.101 x 24 Whitworth tap?

 

[James H Clark]

I suspect that sewing machine factories are like instrument factories, likely to find lots of odd ball taps and other threading equipment lying around. I purchased a small box of odd ball taps from a guy that had just come from an instrument auction. I have never had any use for any of them, but interesting to look at.
JH