K&M 19695-300

These adapters are over engineered to a high degree, but they are robust and sturdy, managing to hold a decent weight condenser on a wall for a god 9-10 months without any sag. The flexible angle mechanism allows for mics to be angled anywhere within a half-spherical radius, and lock in at that position with the thumb screw. The only caviat is that it's a bit pricey for what it is.

Helps to turn microphones upside down or in all kinds of different angles with just a single twist. You don't need to touch the whole microphone stand anymore to position a mic in the last few manoeuvres which saves time when musicians are waiting. ;) Very solid.
Only downside is it can take a little while to get it of the stand again. You have to remember that you better first unscrew it of the stand and then unscrew the mic from it.