What is the max you can shim a muzzle brake? A suppressor will be attached also

I have never seen a max stated anywhere, but most of the people I know, as well as myself, never go past 4 shims. If you need more than 4, you could most likely substitute a couple of them for 1 thicker shim.

hmmm..........1/2 x 28 threads, assuming you are talking about 5.56 barrel, has a thread pitch of .0357. If you used a shim stack that was that thick you would be right back to where you started, as far as indexing goes........so, you wouldn't want to use even that much, unless you are wanting to gain clearance between a rail and your can.
   Are you asking about indexing, or about gaining clearance?

Edit: and inquiring minds want to know.......why the same question reposted after posting 2 hours prior?

I accidentally posted twice right after the other. This will be for a 5/8th thread. And yes it is for rail clearance for a suppressor.

hmmmmmm............I cannot give you any solid information concerning how much thread length you HAVE to have to insure alignment of a can, but I myself would want to have at least thread diameter...........which in your case would be 5/8 length.
  If I were you I would send an inquiry to the manufacturer of your suppressor.   I also vaguely remember YHM having a very informative web site, concerning thread fit class, etc.   You might do a Google search for their site and see if there is anything there concerning your question. HTH