Ned Simmons wrote:
On Wed, 22 Oct 2008 15:07:32 -0700, Jim Stewart
wrote:

I need a reality check. I constructed this
7/8-20 UNEF Class 2A thread from the data I
found in the Machinery's Handbook. I can't
believe that the minor diameter lops so much
off of the lower part of the form. Is this
right?

http://www.grumpyoldgeek.com/images/UNEF_thread.jpg

You should have a flat equal to 1/8 the pitch at the major diameter of
the thread. The thread crests should be truncated to about 1/4 pitch
at the minor diameter. There are good illustrations in MH, several
pages before the tables in my 22nd edition.

OK, I need to put the 1/8 flat on the major
diameter and then the minor diameter should
fall into place.

Also note, that's a 2B thread -- 2A is the external spec.

Got it. Thanks for your help.