Bolt GradesWhen working with fasteners, it is important to know the different types of fasteners, as well as the different grades, so you can select the proper strength bolt for your project.
A Grade 2 bolt is composed of Low or medium carbon steel. A grade 2 bolt will be identified by an absence of markings on the bolt head.
A Grade 5 bolt is composed of medium carbon steel, quenched and tempered. Its tensile strength is 120,000 pounds per square inch. A grade 5 bolt will be identified by 3 radial lines on the bolt head.
A Grade 8 bolt is stronger, made of alloy steel. It has a tensile strength of 150,000 pounds per square inch. A grade 8 bolt will be identified by 6 radial lines on the bolt head.