Drill America 100 degrees countersink is high-speed steel tools are good for most general purpose applications, offering a combination of hardness and toughness for wear resistance. Weldon shanks feature a round shank with one of more flats machined into the side for easy indexing and alignment. Through-hole flute style has a single flute that passes through the cutting head to reduce vibration and chip clogging; also called "zero flute".