I think they edge of the hole is chamfered so look bigger as it is just at the end but not the threads, I am sure they are 6mm though.
Would be worth running a tap down them first with grease on to clear them out, then when done if you leave some bolts in holes with loads of coppaslip it will stop them crudding up again, so next change just remove bolts left in put on puller etc, job jobbed as it were.
Glad to help, no problem at all.
tabetha