Thanks for all the responses and advice!!!

Bill's link, http://www.climaxmetal.com/set_screw_coupling.htm , is
what I had in mind for an insert. Although these would have to be cut
in half. Not a bad idea, that way I would have two inserts.
The more I thought about it, there might be a problem drilling and
matching up the hole in the wood knob exactly where it is on the
insert, and this would be done before I push in the insert. Also
there's a chance of getting CA or epoxy in the tapped hole for the set
screw when I push the insert in the knob.

I like the idea of using a Helicoil. I never heard of those before.
Looks like a great product. Thanks Leo!

One day I may even try these:
http://www.grainger.com/Grainger/ite...Insert-_-4ZB64

I might try to tap a hole in the wood knob and leave out the insert.
Although I know someone who did this and they said the threads
stripped out quickly. However, once the knobs are on the guitar,
there's really no reason to take them on and off. So I might be over
thinking this whole thing. I may even try what Mike said and try a
simple friction fit and see how that works. Do you think the rise/drop
of humidity could make the knobs lose and fall off?

BTW, here's one of the leading guys in the field of wooded guitar
knobs. I have contacted him and all he could tell me was that he
machines his own inserts. One thing that boggles my mind is how does
he powers the LED's in some of his knobs???
Click on gallery to see examples of his work.
http://www.thgknobs.com/

Thanks again guys, I really appreciated all the advice!

Roy