D Series Drill Bits are designed for use with Reed drilling machines and Mueller® E5/D5 only; both of which use saddles. These spiral drill bits are made from strong, high-speed steel, and are heat-treated for longer life. They are black-oxide coated for corrosion resistance, and are much easier cutting than other drills as the spiral motion clears chips away from the cut. D series drill bits are recommended for cast iron and ductile iron, including cement-lined ductile iron.