Correct. Grade 2 has no markings, Grade 5 has three (3) radial lines on the head, and Grade 8 has six (6) radial lines on the head. Metrics should be stamped with an 8.8, 10.9 or 12.9 on the head, as a reference. Some GM bolts are metric as you get to the newer models.Cheap Rotors are low grade steel which warps after u drive down that big hill ONCE. Look up grades of bolts: grade 5, grade 8, etc. are really tough. Buy a bolt from HFreight and watch. U can virtually c it erode away to nothing! I try using grade 8 which I believe has 6? Hash marks on the head, when replacing a stripped, etc. bolt or nut.