Doug White wrote:
Robert Baer wrote in
net:
snip
I nominally use 2-56, 4-40, 6-32; sometimes 8-32, on rare occasion
10-32 then 10-24 and lastly 1/4-20 (been ages since i had to do a lot
of work using 1/4-28 and it was in steel and i may have used 70%
percent of full thread - over 40 years ago).
On all of the common stuff mentioned, i use 75% percent of full
thread since the hardest material i work with is aluminum.

One note: 6-32 is the worst thread to tap. The ratio of the metal you
are removing to the root diamter of the tap is the largest, and they are
very easy to break if you aren't careful. A good tap block will help a
lot. For 1/4-20, you can make your own. If you do a lot of tapping, do
yourself a favor & get a commercial guide block or guided tap wrench.
There are several to choose from. For electronics work where you
frequently need to get into small spaces, I prefer one with removable
sleeves, but the one I have doesn't appear to be available anymore.
Here's a collection of tapping tools, including an inexpensive block:

http://tool.wttool.com/tools/Tap%20Guide

Here's one that looks like it will work well in tight spots, and has a V-
groove on the bottom for tapping round stock:

http://littlemachineshop.com/product...ProductID=3427

Doug White


6-32 is the size i work with the most; never had a problem.
But i have broken a few 2-45 taps (they are delicate).