How to Identify Bolt Grades & Materials

Written by floyd drake iii | 13/05/2017
How to Identify Bolt Grades & Materials
Bolts, screws, studs and nuts are all graded according to SAE standards. (Jupiterimages/ Images)

While they may look the same, bolts and other fastener types are different. Bolts are graded by their strength and the materials used in the casting process determine the strength for each grade. Bolt strength grades are determined by the Society of American Engineers, or SAE, who also determine the materials necessary for each grade of fastener, and the strength ratings of each bolt grade. Grading bolts is a simple process and by looking up the specific bolt grade, the materials used in the forging process can be determined.

Identify the markings on the bolt head. The bolt head has six sides and there will be a series of lines starting at the centre and pointing to the sides. There will be no lines, three lines or six lines, depending on the bolt grade.

Determine the bolt grade. No lines indicates a grade two bolt, three lines identifies a grade five bolt while six lines is a grade eight bolt.

Identify the materials used in the bolt forging process. The metals used are standardised and can be simply identified. According to the grading chart found on the Bolt Depot site, SAE grade-two bolts consist of low or medium grade carbon steel, grade-five bolts are forged with quenched and tempered medium-carbon steel while grade-eight bolts are forged with quenched and tempered medium carbon-alloy steel.

Determine if the bolt is stainless steel. Stainless steel bolts do not have standardised markings for identification. However, stainless bolts are non-magnetic and are not attracted to magnetised wrenches or magnets. Stainless steel bolts are comprised of a steel alloy with 17 to 19-percent Chromium and eight to 13-percent Nickel, according to the Bolt Depot.

Things you need

  • Magnetised wrench, or a magnet

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