Thanks for the link, it's a nice discussion. I especially liked the photos.
I didn't mean to imply that the forming process would bulge less than the cut threads in an unsupported thin wall. I meant that a supported wall would bulge less than an unsupported wall and that thread forming was still an option if the thing was clamped in a vise to support the wall. I still think that's the case.
> > Thread forming taps won't make chips. If the wall of the part is
> > supported in the vise, bulge should be minimal.
> Thread forming taps make more of a bulge than cutting ones because
> they have to shove the material around (hence, "thread forming" as
> opposed to "thread cutting"). This shoving around of material is
> also why you have to countersink the holes to avoid getting a lip at
> the material surface(s).
> They do not work well in thin-wall material; they make a much larger
> bulge. (Voice of experience here.)