1999 GMC 1/2 ton PU, 5.3, 112,000 miles auto trans with ABS. What size allen wrench do I use to remove the brake calipers? An 8mm is too small and a 9mm is too big. Also a 5/16 is too small and a 3/8 is too big. Is there a special GM tool for this? This is the front, the back has hex head bolts. Thanks