Thunderbolt drill bits are designed for use with cordless and other portable drills. The bits are engineered with a thicker web and unique flute form which allows for quicker penetration and improved drilling times. With increased strength built into the web, the Thunderbolt bit can perform many operations where conventional bits break. The open flute form ejects chips more efficiently when drilling deep holes which helps prevent lock-ups at breakthrough. Black and bronze high speed steel provides heat resistance, durability and increases bit life. Features: Milwaukee 48-89-1120 20 Piece Thunderbolt Black and Bronze Drill Bit Set Thunderbolt web for increased strength Open flute design for efficient chip ejection Faster spiral for improved drilling times Black and bronze finish reduces friction keeping the bit cooler