I this the single serpentine set up your working on? If so, are you trying to get the pulley off? Do not mistake hex bolts for socket head bolts. If they are hex bolts and they are rounded off try a pair of ChannelLock Modle 410 stud pliers. If this proves unsuccessful I would use an air hammer with a flat blade chisle. I prefer the Snap On model PH3050 with a 7" chisel model, PGH55A. Try to get a bit on an edge an rotate the bolt out counter clockwise, you have to be gentle on the trigger, until it's loose enough to spin out with your fingers.