The grade 8 steel hex bolt has a zinc yellow-chromate plated finish and an external hex drive, and meets American Society of Mechanical Engineers ASME B18.2.1 and Society of Automotive Engineers SAE J429 specifications. Grade 8 steel, composed of quenched and tempered medium carbon alloy steel, is stronger than grade 5 steel and is often used in applications where strength is the primary concern. The material is magnetic. The zinc yellow-chromate plating offers good corrosion resistance. The external hex drive has six flat sides that a wrench can grip to turn the screw from the side, enabling use when there is no space above the head for a driver.
Cap screws and hex bolts are threaded fasteners with thick hex-shaped heads that can be used with threaded nuts or in areas with limited clearance above the tapped (threaded) hole. Cap screws have slightly different dimensions than hex bolts and have a washer face underneath their unflanged hex head to act as a large bearing surface against the mating material.