horseydug -
I tried every size from 10 to 19 mm, I have a complete set of SAE and Metric sockets. It seems like somewhere around 15 or 16 should work, but it ends up that the socket is too small to fit on the bolt, or the socket is too big to fit in the hole in the pulley.. I don't see why this is, I'm using 3/8" drive sockets, and the sides aren't very thick.... Maybe I need sockets with even thinner walls (i.e. the socket's OD is smaller for the same bolt size), and it's just a tight fit.
