Grade 8 bolts have been hardened more than grade 5 bolts. Thus they are stonger and are used in demanding applications such as automotive suspensions. Grade 8 bolts have 6 evenly spaced radial lines on the head.
Specifications: Gr. 5: SAE J995 USS 120,000 psi, SAE 109,000 psi Gr. 8: SAE J99
