Should be 10mm or 3/8ths
Actually, it turned out to be 7mm Allen wrench.
I believe it is a 7mm hex.
Loosen and remove the caliper retaining bolts. Torx T-40 or T-45
7MM
Bolts on the caliper of a 1999 Monte Carlo will loosen to the left and tighten to the right.
The caliper bolts can be accessed from the rear of the caliper. After removing the tire you can view the recessed brake caliper bolts. You will need a large Allen wrench, as these are Allen head bolts. Consult your auto parts store for the proper size Allen wrench. Common toolbox wrenches will be far too small. I would advise to spray down with some WD-40 the night before. You should also make available a large hammer to hit the wrench and loosen the bolts, as it is an akward position to muscle the bolt free with a short wrench.
For the caliper mount bolts that are removed during a brake pad change, 1/2" is a good fit on my 1996 F250. 13mm will fit but is a little sloppy. Were you asking about the "caliper bracket" instead?
You need a 'Star' or 'Torx' wrench. The rubber collars keep dirt of the caliper mounting bolts so the caliper can 'float'
A 3/8" Allen wrench is used to r&r the caliper bolts.
the caliper bracket bolts use 18 mm wrench on a 03 1/2 ton 4x4
A box wrench has a closed end and is used to tighten or loosen nuts or bolts.
The Allen wrench size for the front caliper slide pin bolts is 3/8".
the caliper bolts require a 3/8" Allen wrench. You can buy these as a socket at just about any parts store.