Milwaukee 21/64" Thunderbolt Black Oxide drill bits are engineered for extreme durability and long-lasting performance. Featuring the Thunderbolt® web with a thicker core than standard drill bits, they strength and resistance to side-load breakage. The specially designed parabolic flute efficiently clears chips and debris to keep the bit cool during use. With a precision start 135-degree split point tip, these drill bits begin on contact and prevent walking for fast, accurate holes. They are excellent for drilling on curved surfaces, require less effort, and are highly for use with portable drills. Model Number: 48-89-2727