I don't believe that bolt grade matters. The failure mode is in the bolt (shaft). Type of nut or threaded holes are irrelevant in terms of fastener failure.
I need to pick up some grade 2 bolts - where do I find them??
JayC
Why would you screw a 150,000 psi bolt [grade 8] into a 120,000 psi [grade 5] or a 60,000psi [grade 2] nut and risk the bolt pulling through the nut?
Soft washers are useless; they just squeeze out from under the bolt head. Under dynamic loading the bolts per-load will be lost.