All bits in this Faithfull Metric 19 Piece HSS Jobber Drill Bit Set are made with a black oxide coating, manufactured from HSS in accordance with the DIN338 standard. Suitable for use in alloy steels, carbon steels and hardened alloy steel - and although designed for cutting metal, you can also use in plastic, timber, chipboard and plywood too for ultimate versatility. Cutting lubricant recommended.