On Sun, 05 Apr 2015 07:47:14 -0500, Ignoramus10114
wrote:

I have an aluminum heatsink that I need to tap , I wanted to know if I
should use 6-32 or some less coarse thread like 8-32 would be better?

Always tap aluminum that will be stressed ..as course as possible.

Particularly in thing sections or places where you will not be using
more than 2x/diameter.. of depth