APR head bolts

[Ruan]

Remember theyre not just high tensile, its all about the heat treatment they undergo, also you cannot cut the threads, they must be rolled on as you seriously weaken the threads when cut vs rolled... You significantly increase strength with rolled threads, you'll probably pull the threads off the stud if they're not rolled...

There's a great article on head studs somewhere explaining about the heat treatment process and why solid studs are a worse design, but solve a lot of the problems that we get with high cylinder pressure...

Fastners are an incredibly complex art, not just any old bolt that's strong...