The 15-Piece Thunderbolt® Black Oxide Drill Bit Set offers convenience and heavy-duty performance on the jobsite. Milwaukee® Thunderbolt Black Oxide drill bits are designed for extreme durability and long life. The Thunderbolt web features a thicker core than a standard drill bit to provide ultimate strength and protect against side-load breakage. A specially designed parabolic flute form clears chips fast, while the 3-Flat Secure-Grip™ shank holds the bit firmly in the drill chuck. The 135 deg split point tip delivers a precision start and prevents walking for fast, accurate holes. Effective for drilling on curved surfaces, Milwaukee Thunderbolt Black Oxide bits require less effort to drill through metal, wood and PVC and are highly recommended for use with portable drills. Thicker web provides greater strength and longer life 135 deg split point tip starts on contact to prevent walking, while the parabolic flute clears chips fast 3-Flat Secure-Grip™ shank holds the bit firmly in the chuck Black oxide coating provides lubricity and resists corrosion of the bit