My granddaughter will be with me tomorrow and I may miss your post, so I'll give you what information I have, now.
Grade 1 or 2 won't have any hash marks on the head. Grade 5 will have 3 hash marks and Grade 8 will have 6 hash marks. These are US standard SAE.
Bolt strength head markings for metric are:
4.6, 4.8, 5.8, 8.8, 9.8, and 10.9.
Torque Specs for Metric in Nm/Ft-lb:
M-6, 9-12, / 6-9
M-8, 19-28 / 14-21
M-10, 38-54 / 28-40
M-12, 68-96 / 50-71
M-14, 109-154 / 80-140
I find it odd that there's big gaps between the various sizes.