How can you identify the grade of a bolt?

The grade of a bolt is identified primarily through the markings on its head, which usually indicate the strength and material properties of the bolt. These markings can include a combination of numbers, symbols, and manufacturer identifiers that correspond to specific grades defined by standards such as ASTM (American Society for Testing and Materials) or ISO (International Organization for Standardization). For example, a bolt with three radial lines indicates that it is a Grade 8 bolt, which has a specific tensile strength and performance capability.

This method is standardized and allows for quick identification of bolt specifications without the need for additional tools or measurements. While measuring diameter may give an indication of size and application type may hint at the appropriate usage, neither provides definitive information about the strength or quality that is as clear and regulated as the markings on the bolt head. The color of the metal can vary based on plating and does not relate to the mechanical properties or grade of the bolt.