Tim speaks wisely, but i would have assumed that these bolts are metric therefore the grading is 8.8 ...10.9....or 12.9 ....... 8.8 being close to to sae Grd 5 in carbon content..
Be careful replacing fasteners with higher grades than spec , they become springs in the way that they are torqued and will not perform as well with torque designed for a lower grade.
Graded fasteners are so for a reason, going to a higher grade does not guarantee quality as to function by design.
SS fasteners major purpose is for application in the marine or high humidity environments they come in different grades as to the severity of this , and also gain some strength at the same time ..
SS as a rule does not like Aluminum ,it depends on the alum, but bonding can occur so be careful..
If your stripping out the heads of your fasteners often , then it probably means your hex keys are wore or they are new crap to begin with ..they should fit tight so they apply even torque to the drive.. buy Bondus they are PDG... T handles are the ticket