Grade 5 Bolt Specifications

Industry rates bolts in many different ways. The Society of Automotive Engineers (SAE) ratings differ slightly from those of ASTM International (originally known as the American Society for Testing and Materials). The International Standards Organization provides a separate rating system for bolts that is stricter than ASTM and SAE. Bolts come in many sizes and strengths. The grade of a bolt depends on its strength. Grade 5 bolts typically connect metal to metal.

Proof load measures the direct load (tension applied) that a fastener must support without visible distortion. This measurement is given in pounds per square inch (psi). The proof load specification for a Grade 5 bolt is 85,000 psi for bolts 1/4- to 1-inch long. Bolts over 1 to 1.5 inches long must endure a proof load of 74,000 psi. The ASTM requires the proof load specification for a Grade 5 bolt to be 55,000 psi for bolts from over 1.5 to 3 inches. The equivalent ISO bolt is an 8.8 and must proof load 85,000 psi for all bolt sizes.

Yield strength measures the direct load (tension applied) that a fastener must support with a specific amount of visible distortion. This measurement is also given in pounds per square inch. The yield strength specification for a Grade 5 bolt is 92,000 psi for bolts 1/4- to 1-inch long. Bolts over 1 to 1.5 inches long must endure a yield strength of 81,000 psi. The ASTM requires the yield strength specification for a Grade 5 bolt to be 58,000 psi for bolts from over 1.5 to 3 inches. The equivalent ISO bolt must have yield strength of 92,000 psi for all bolt sizes.

Tensile strength measures the amount of resistance a material provides against any force attempting to stretch, deform or tear it apart. A Grade 5 bolt tensile strength is 120,000 psi for bolts 1/4- to 1-inch long. Bolts over 1 to 1.5 inches long must provide a tensile strength of 105,000 psi. The ASTM tensile strength specification for a Grade 5 bolt is 90,000 psi for bolts from over 1.5 to 3 inches. The equivalent ISO bolt must have tensile strength of 120,000 psi for all blot sizes.

The rating of each bolt depends upon bolt length. As noted previously, the size of the bolt determines the requirements for proof load, yield and tensile strength.

Markings on the bolt head help to identify the bolt rating. A Grade 5 bolt is identified by three lines radiating from three points equidistant around the bolt head circumference into the center. The ISO equivalent, Grade 8.8, shows the number 8.8 or 88 stamped upon the bolt head.