The 21-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.