Phillips pan head sheet metal screws have sharp threads designed to cut into sheet metal, plastic and wood. These screws are fully threaded which provides good retention in wood. These screws are commonly used to attach metal to wood materials. Once screwed in, the pan head will of the screw will sit above the surface. Black Oxide sheet metal screws have been chemically treated to alter certain qualities of the material, most notably the color. The treatment also adds a mild corrosion and abrasion resistance (in addition to the plain stainless steel's nature), and reduces the now black oxide stainless steel fastener's reflective properties.