The plastic threads on my Schoeps a20s always worried me. That's an expensive mount to toss in the garbage just because the plastic threads got worn out. Here's my solution:
Assuming you want to keep the 5/8-27 mic thread, get a 5/8>3/8 adapter and a 3/8>5/8 adapter (they can be had here: http://www.micsupply.com/standaccessories.htm
as well as B&H photo and a numer of other places).
Prep the threaded areas of all three pieces by cleaning them w/ rubbing alcohol. Let dry. Apply Thread-Loc or similar product (can be had in an automotive store) to the 3/8" male stud of your 5/8>3/8 adapter. Firmly screw on your 3/8>5/8 adapter. Allow Thread-Loc to set over night.
Now apply some Thread-Loc to the male stud of what is now your 5/8f>5/8m adapter. Screw firmly into your shock mount. Allow to set over night.
Congratulations, your a20s or similar mount now has metal threads!
Taking things one step further, I wanted to nix the silver finish of the adapter so I just wrapped it in black electrical tape after everything had set. I suppose you could also spray paint it too...
Hope this helps someone.