What Is a Hardened Bolt

Grade 5 bolts are case hardened, meaning the bolt has been heated enough to hardened the outside of the bolt but not enough to harden the inside portion. Grade 5 bolts are identified by 3 evenly spaced radial lines on the head.

How can you tell if a bolt is hardened?

You can usually figure out the grade, or strength, of a bolt by looking at the markings on its head. English bolts (U.S.S. or S.A.E) are categorized by grade, from grade 2 to grade 8, where the grade represents inch strength. The higher the grade, the stronger the bolt.

Is 8.8 bolt hardened?

Class 8.8 is hardened, but it is not as strong as class 10.9. It is commonly found in automotive applications. Class 8.8 is similar to grade 5. Zinc plated for moderate corrosion resistance.