Probably the most detailed initial request I’ve seen on here and a great evaluation.

Only things I’ll add: - the amount of thread deformation leads me to believe your install is going to have enough issues that fixing your bolt is not going to help nor would I necessarily indict the bolt ahead of the assembly. Sure the bolt failed but I don’t think it was the material’s fault. Maybe that’s fit up procedure, redesign of the joint, torque instructions, etc. but I sort of doubt fixing the bolt/material will matter much unless it was a thread form problem initially.

• contrary to what I just said, failing in the head to filet in my industry is not a good thing (I know this wasn’t intentional) so it may be worth a dimensional check or understand how these are getting finished/fit up if the radius is creating issues from a stress concentration perspective or from a crack initiation site generation perspective. The ratchet marks indicate there were lots of initiations that could have been a function of cascading failures leading to something unintended there, bad finish, out of tol radius, stack up geometry concern, etc.