It's a 15mm. I wouldn't use sockets or air tools; instead use a 15mm box-end wrench. Loosen the bolt by hitting the wrench with a hammer right below the head (on the wood); make sure the wrench doesn't slip off. You might scar the handle some but oh well.
You'll need big channel-lock pliers or a c-clamp to push the piston back into the caliper. A large-ish screwdriver will be needed to initally loosen the pad from the rotor. I'm pretty sure these are the only tools I used to remove my caliper. It took me about 15 minutes after getting the wheel off.
Oh the official torque specs for the caliper bolts (2) is 92 ft-lbs if you're keeping track.
