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270677 Erik Levin 2020‑04‑30 Re: Threading die for 0.108-50
Thanks to those that got back to me with bits of info. To address John's
questions:


They are lock screws for long-reach internal micrometers (fixed range type. One
screw remains for the entire set), and two screws for a vernier caliper (24". It
also came with only one screw), all WW-II vintage. Metric is unlikely, as even
the metric B&S tools, in my experience, had imperial fasteners and fittings at
that time. The diameter is also not close enough to a metric to be a match,
either in standard or miniature. This is, obviously, not critical, but as I have
needed to swap these around a few times for use, I know I will eventually lose
one. These are user tools, and see life in the field, though they don't live in
my fieldwork kit.


I haven't eliminated 7/64, per se, but I think #4 is definitely too large at
0.112". The 0.108 screw is quite a neat fit, and there is little play in the
0.106. There are 10 holes for these screws, and the fits are pretty much the
same for all.


Most assuredly 50TPI. B&S, like Starrett, used their own sizes and pitches for
many things, especially smaller sizes. For example, the 0.110-52 screws Starrett
has used in the #154 adjustable parallel for many many years (not a match. I
tried one just to see). Measured the pitch with thread gauge, confirmed on the
optical comparator. 50 matches, 48 and 52 decidedly don't. 60 degree vee. I
didn't check the pitch diameter with wires, though will when I get the time. I
don't have 0.016 wires (0.020 is just too large) so will need to find my spare
gauge pins.


Yup. The comparator is most assuredly old-tool status at this point, but not as
old as the traveling microscope.


There are many threads I don't mind single pointing. These are small enough I
really don't want to deal with them, and 50TPI is not a standard thread on my
lathe. Some of the Stanley threads are pushing it, but at least they are more
accessible pitches.



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     On Thursday, April 30, 2020, 10:48:31 AM EDT, John Ruth 
wrote:
 
 Erik,

You deserve more than the sound of the crickets after posting this “juicy”
obscure question.  So, in the interest of at least attracting more attention to
your quest:

Given the diameters you’ve measured, how did you eliminate size #4 and size
7/64ths as possible “nominal sizes?”

Sellers proposed/listed standard pitches for tiny fractional sizes including
7/64ths, but 50 tpi is not among them.

Have you considered the remote possibility that it’s Metric?  It’s “almost” a
pitch of 0.5mm.

IIRC, you have access and expertise on an Optical Comparator, which has become
an old tool in its own right.  And, your post certainly shows ability to perform
precision fine measurements.

“Grasping at Straws:” Can the thread profile be recognized as any particular
standard system?

Erik certainly provided impetus for wandering far out into the tall grass beyond
left field:  the 1959 re-definition of an inch was considered when pondering the
question of whether 50tpi is a round decimal in metric...no, that change only
shortened  the old US inch by two millionths of an inch!

John Ruth
“Of threads, and threading systems, there is no end!”

Recent Bios FAQ