What distinguishes an SAE grade 5 bolt from grade 1 or 2?

An SAE grade 5 bolt is distinguished by the three radial lines on its head, which indicate its medium strength compared to grade 1 or grade 2 bolts. These markings help identify the bolt’s grade and its applicable uses in industry.

Grade 1 bolts are generally made of low carbon steel and have no markings, signifying that they are the weakest among the SAE grades. Grade 2 bolts may have a single line or no lines but do not have the distinct three lines that denote grade 5. The presence of three lines for grade 5 emphasizes its higher tensile strength and ability to withstand greater loads, which is essential in applications where medium strength fasteners are required. The distinguishable markings on the head thus serve as a quick reference for engineers and technicians selecting the appropriate bolt grade for their projects.