On Wed, 9 Jul 2008 05:04:33 -0700 (PDT), Jim Wilkins
wrote:


The thread OD on my collets measures from 1.220 - 1.230 for Enco to
~1.243 for R-S-B. I made a collet nut for an S&D drill grinding
fixture that fits closely on a 1.240 thread. Some of the R-S-B collets
are too tight for it.

Don't confuse the thread's nominal size with its major diameter. The
major diameter is generally a bit below the nominal with a pretty
generous tolerance. For example, the major diameter of a 1.250-20
UN-2A is 1.2486/1.2405.

Ned Simmons

--
Ned Simmons