arp stock bolts on 7mgte?

i have 2 7mgtes that im rebuilding. i went to take the head off and all the stock bolts where arp 12 point metric 12mm "on both engines"!! i thoght that the stock head bolts where 10m allen? why are all the bolts arp dose it just so happen that i have 2 engines that have upgraded bolts or did arp bolts come from the factory?