How to Identify a Grade 8 Bolt

by K.K. Lowell

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.


  • check Don't consider the color of the bolt when identifying bolt grades. Bolts can be plated without affecting hardness or grade.

Items you will need

About the Author

K.K. Lowell is a freelance writer who has been writing professionally since June 2008, with articles appearing on various websites. A mechanic and truck driver for more than 40 years, Lowell is able to write knowledgeably on many automotive and mechanical subjects. He is currently pursuing a degree in English.

More Articles