On Sun, 14 Jul 2013 22:06:34 -0400, "Jim Wilkins"
wrote:

"John B." wrote in message
.. .
On Sun, 14 Jul 2013 11:11:46 -0500, "Terry Coombs"

wrote:
"Paul K. Dickman" wrote in message
...


There is something wrong with your logic. Ignoring the question of
what fits what I believe you will find that all taps cut a larger
diameter then the nominal size of the fastener. If, for example you
were to thread a 10 mm rod in the lathe and than drilled and tapped
a
10 mm hole the male rod, being 10 mm must be threaded into a larger
hole, otherwise it would be an interference fit and damned hard to
screw in :-)
John B.

This one is easy to check. I measured a few 1/4" and 3/8" Greenfield
taps at 0.0015 - 0.002" under the nominal diameter.
jsw


Then they won't cut proper UN threads. The *minimum* major diameter
for 1/4-20 UNC - 2B (and 1B & 3B) internal threads is .2500. Likewise,
the minimum major diameter is equal to the nominal size (the basic
major diameter) for all 1B, 2B and 3B UN threads. Similar rules apply
to metric threads.

--
Ned Simmons