with a little research I found this:
hope it opens for you as it shows the bolt hardness markings
so currently I have a grade 5 bolt in the shear bolt location.
but the two bolts that I have in my tractor tool box for backup replacement shear bolts are grade 8.
so I need to buy softer replacement bolts as backups.
Thanks for your help on this:
replacing a soft shear bolt is much easier than replacing a busted gear.