Lots of current engines use head bolts w/an Allen or Triple-square head on them, unfortunately they are all metric, and most are much longer than older apps. The ones
above would be triple-squares which require like bits, and excellent quality ones at that. Hyundai/Kia and others are using the same, and they are all TTY fasteners.
Go to McMaster-Carr and look up reduced head fasteners, they are made for these very situations.....................................
Someone else already mentioned ARP, those are reduced hex-headed......
