Use What You Have (Material is Everywhere)

[Janderso]

MotorTrend TV just re-ran episode 16-4 of Wheeler Dealers: 2001 Saab 9-3 Viggen had a head leak that was addressed by replacing the original head bolts (hardened) with torque-to-yield bolts that were specified by Saab to correct an issue where the hardened bolts would loosed since they didn't stretch when torqued. If the Cat bolts are torque-to-yield they would have a lower tensile strength than hardened bolts and in order to be torqued reliably would only be used once (not a bad idea for head bolts in general):

https://en.wikipedia.org/wiki/Torque-to-yield_fastener

I saw this more and more on Ford products as the years went bye.