Machine screws are generally used to fasten metal parts together in various types of machinery, automotive, and construction applications. Machine screws are typically used with a pre-tapped hole or with a nut. 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 slotted drive has a straight-line notch grooved into the surface the head and is designed to be used with flat-headed screwdrivers. Zinc plated steel offers good corrosion resistance in applications not exposed to excessive moisture.