These are M42, high speed steel with 8% cobalt. This material has excellent abrasion resistance for improved tool life. It is a good choice for machining cast iron. Used for general milling operations, centre cutting, two flute slot drills can plunge cut and then mill a slot. Two flute cutters are able to remove a high volume of material allowing them to run at high production rates. They have round shanks with a flat (DIN1835B) and are suitable for use in ER collets.