BOLT, 5/16-18 X 1-1/2 hex. hd.  1x

grade 8 bolt 

Made from Grade 8 steel, these screws can be used in high-stress applications, such as valves, pumps, motors, and automotive suspension systems. They are at least 25% stronger than medium-strength steel screws. Grade 8 steel hex head screws are marked with six radial lines. Length is measured from under the head.

Zinc yellow-chromate plated steel screws resist corrosion in wet environments