Grade 8 bolts are specified for high strength applications and should not be replaced with regular bolts or bolts of a lesser hardness grade. The system used to mark the heads of bolts with simple symbols makes identifying the various grades of bolts easy to learn and remember.
Try to pick up the bolt with a magnet. Grade 8 bolts are not made of stainless steel and will be attracted to the magnet; stainless bolts will not be attracted to the magnet.
Clean the head of the bolt with a wire brush to see if any bolt markings are present.
Examine the head of the bolt and count the radial lines. Grade 8 bolts have six radial lines and no numbers. The absence of radial lines indicates a regular bolt; three radial lines indicates a Grade 5 bolt.
