Self-tapping screws create their own threads but require a pilot hole. The hex head washer has an external hex head with a washer-style flange attached underneath the head which creates a large surface connection area. Hex heads protrude above the surface. The externally driven head allows greater torque to be applied to the screw compared to other screws that are internally driven. Indentation on the surface of the head is preferred for applications involving power-driving tools. The external hex drive is designed to be used with a ratchet. 18-8 stainless steel, also commonly known as 304 or A2 stainless steel, has good chemical resistance and may be mildly magnetic. The black oxide coating greatly reduces the risk of hydrogen embrittlement.