Drillco 5 piece reduced shank S and D drill set. The Nitro 118 degree split point S and D drill with nitride surface treatment, that gives hard, protective layer to the drill (increases hardness without increasing brittleness), which is measurably harder than High-Speed Steel. Body and clearance are black and gold surface treated for maximum lubricity. Recommended for use in stainless steel and other hard metal drilling. The 118 degree split point reduces thrust and eliminates walking at the drill point. High-speed steel tools are good for most general purpose applications, offering a combination of hardness and toughness for wear resistance. Black oxide treatment adds lubricity and creates small pockets on the surface of the tool that act to hold coolant near the cutting edge. Gold oxide is a thinner oxide surface treatment than black oxide typically used to identify cobalt steel tools; performance is similar to uncoated tools. Round shanks allow use with a wide variety of toolholding systems. When run in a counterclockwise direction (right-hand cut) spiral fluted tools evacuate chips up and out of the cut to reduce clogging.