Welcome and the grade 2 is the weakest then it goes to grade 5 with 3 lines on the head then to grade 8 with 6 lines on the head and are usually yellow/gold in color
Jim
Can't tell you the difference. But I can tell you to use the shear bolt that the manufacturer sells for the machine, as long as the machine is still in the warranty period, or you'll void the warranty. Sometimes an unmarked bolt will stretch and bend, but not shear. Amazing how a 10 cent part can sometimes outlast an expensive, complicated mechanism!