This tool sounds like it will fit MORE 10mm and 13mm screw heads but not 13mm screw heads. not even close!. I used it on my 2002 Olds Bravada (4.2L engine) as do most Outriders, Envoys etc so I simply removed 2 bolts (13mm) this tool into the open holes on the water pump pulley plugged in and then backed off the 2 bolts while holding the tool, used my giant adjustable wrench on the fan clutch nut, held both in place and used a little muscle strength. freed! I was so happy! But please revise the