Well, follow up time:
I borrowed a little time on an unmentionable machine with a brain of sorts, and
made up some test parts.
Things I was sure of:
-Thread pitch is 50TPI
-Thread for on the screws I had in hand was 60 degree vee. I don't have an
appropriate profile measuring way to accurately profile an internal thread this
small, so will figure it is as well.
-The OD is within a few thousands of an inch of 0.108", and the thread may be a
I ran test pieces in sizes from 0.105"OD to 0.112"OD (#4), with sharp root
(0.001" or less, by the tool and by inspecting after) to avoid binding, and ran
with the nominal 1/8 of pitch flat at the top (0.0025")
For most of the tools, the 7/64" threaded in snugly, but in a couple, it
wouldn't start (no burrs on the female threads) 0.108" started in all but was
too tight in one, but the 0.107" ran in all of them fine. A tad loose in a
So, I went with 0.107 for the final parts.
Manual work (Fine Arkansas stone) to lightly round the tips, and I used a manual
knurling tool (looks like a tubing cutter) to knurl the stock, as the the
unmentionable machine was not set up to do it and it is about half a day to
Picture of one at: https://
This one I tried knurling at the end, thinking that holding the material to cut
and thread would damage it, and it was a mistake. The rest were done at the
beginning on raw stock.
Thanks for the input on this.
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