Flat Head Socket Cap Screws length is measured in their entirety, which is from the top of the head to the tip. A flat head is cone shaped for use in countersunk holes and has a flat top that fits flush with the mated surface. Stainless steel socket cap screw has a plain finish and a flat head with an internal hex drive. Stainless steel resists corrosion and may be magnetic. The flat head is cone shaped for use in countersunk holes and has a flat top that fits flush with the mated surface. The internal hex drive, also known as a hex-socket drive, has a hexagonal slot that requires an Allen key driver, also known as a hex key or Allen wrench.Black Oxide, blackening, oxidizing, oxiding, black passivating, gun bluing. These terms all refer to the process of forming a black iron oxide on the surface of ferrous metals. Black oxide is a conversion coating formed by a chemical reaction produced when parts are immersed in the alkaline aqueous salt solution operated at approximately 285 degrees F. The reaction between the iron of the ferrous alloy and the hot oxide bath produces a magnitite (Fe3 O4) on the actual surface of the part. The black oxide process is a chemical conversion coating. This means that the black oxide is not deposited on the surface of the substrate like nickel or zinc electroplating. Instead, the black oxide coating is produced by a chemical reaction between the iron on the surface of the ferrous metal and the oxidizing salts present in the black oxide solution. These oxidizing salts include penetrates, catalysts, activators and proprietary additives which all take part in the chemical reaction. The result of this chemical reaction is the formation of black iron oxide, magnetite (Fe3O4), on the surface of the metal being coated. Black oxide has a range of unique properties and benefits that can be applied to a variety of industries.