theres no WAY that they are 6mm bolts, i can guarantee you that. im going to go check right now.
EDIT; yup, iim right... again. i took a 6mm bolt (10mm head) and it slips in w/ no thread engagment. i tried the 8mm bolt (12mm head) like i previously mentioned, and it threads in. grab a pair of long 8mm diameter bolts and run them into the pully. youll probably want to grab an 8mm thread chaser from all the dirt and grime coating the threads inside the pulley. if you dont, the bolt will gall and probalby seize and possibly shear off... then youll be up shit creek w/o a paddle.