Just put a Moser 12-bolt in my car, and noticed that the fill plug has what looks like a 14mm hex plug in it.
My question is where can I get a 14mm allen wrench? Nobody around here has it? I used a bolt and two nuts to make my own "custom tool" but it's kind of a pain.
Another thing; is it the same size as the larger of the two standard diff plug sizes? (I can't think of actual dimensions right now, but I remember there are 2 main sizes). If it is, I'll probably just stick one with a 3/8 or 1/2 square drive hole in it.

 

A 9/16 allen wrench fits mine. I don't know where it came from, but it was in my garage.