My CAC9 like all of them will not stay on my Mac11/9 to save my life due to the coarse thread..
I would like to use it on my M16 with a 9mm upper but I am not going to build an upper around that nasty coarse thread..

Anyway, my question...
Is there anyway to have the threaded section of the supressor cut off and add a new piece that is a finer thread or even 3 lug if possible..

I cant even remember that last time I used it due to this...
Thanks

You have a couple of options.  The best would probably be to contact Tom Bowers about changing out the mount.  He does offer that can with a 1/2-28 mount.  

You could then get a 3-lug adapter and screw it in to the new mount.

I have a few thread adapters for my CAC45, and shoot it on several different firearms.  Of course, there is still the coarse thread that the adapter screws to.  To take care of this problem, I drilled and installed a roll pin through the threads of the can.  Now the coarse threads won't unscrew.  It acts like it only has the fine threads.

It probably voids the warranty, but I feel it's a pretty safe bet.  That, and I'm shooting smaller calibers through the can than it was designed for (9mm, .300 Whisper, and .22LR), so I have a bit bigger margin of error.

Here's a picture before I trimmed the roll pin, so you get an idea.