The class 8.8 steel cap screw has a yellow zinc plated finish, has a serrated flange hex head with an external hex drive, and meets Deutsches Institut für Normung DIN 6921 specifications. Class 8.8 steel, composed of quenched and tempered medium carbon steel, is often used in applications where strength is the primary concern. The material is magnetic. The zinc plating offers corrosion resistance and has a yellow reflective appearance. The flange hex head has six flat sides that a wrench can grip to turn from the side, enabling use when there is no space above the head for a screwdriver. The serrated flange acts like a washer to increase the fastener's bearing surface and distribute the clamping force over a larger area, providing a grip that resists loosening.
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.