Soft or hard bolts for exhaust flange?

I agree with ntsqd above. ESPECIALLY if you are using through-- bolts in the flanges as he's pictured, if one of those seizes up, grade 8 just makes it impossible to remove. At least with grade 2/ 5 you have a chance at twisting the bolt off and then it just falls out.

Hell the bolts in my Hedmans (coming off) collectors are 3/8!!!! Grade 2 would be plenty strong