Just do the simple thing. Buy a set of imperial and metric hex keys. When you have to use one, just try them. If metric won't fit, there will be an imperial once that does. See, simples!
my advice...get the hex key that comes with the bridge and tape it to your headstock!
or better still, get one of those little Gotoh or Schaller key holders, screw it onto the back of your headstock (i can hear all you collectors and anal types saying 'no way!!') and you'll never lose it. i have two badass II bridges and i still have the original keys