Black steel fittings connect to black steel or black iron pipe and pipe nipples for transporting gas and water, protecting electrical wiring, or delivering high-pressure steam and air. Uncoated black steel, also called black malleable iron, is made from corrosion-resistant ungalvanized steel and includes a scaly, dark-colored iron oxide coating on the surface. Black pipe, pipe nipples, and fittings come in a variety of sizes and shapes.