I needed a Hex 9MM worked great
9mm hex socket bit
mercury mariner
Change wheel bearing on 2006 mercury mariner
On the inboard side of the caliper.
The easiest way is with a "C" clamp.
Each of the calipers is held in place by two bolts. Remove the bolts and then the caliper. If necessary you may need to retract the caliper piston using a screwdriver or large C-clamp.
It takes a T55 Torx bit on the front calipers.
Remove the front wheel. Loosen and remove the two 15 or 17 mm bolts securing the calipers in place (access from the back side of the calipers). Lift the calipers out of the way and your rotor will be somewhat loose. Pull off the rotor.
Your local parts store should be able to help / answer that question.
The 2000 Mercury Sable starter will have three retaining bolts. There will be two cable retaining nuts on the front of the starter.
Why not just try different size sockets until you find the correct size.