The class 10.9 steel cap screw has a phosphate and oil finish, has a non-serrated flange hex head with an external hex drive, and meets Deutsches Institut fr Normung DIN 6921 specifications. Class 10.9 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 phosphate and oil coating provides corrosion resistance and lubricity. The flange hex head has six flat sides that wrenches can grip to turn from the side, enabling use when there is no space above the head for a screwdriver. The non-serrated flange acts like a washer to increase the fastener's bearing surface and distribute the clamping force over a larger area, providing grip and reducing damage to mating surfaces. 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.