Milwaukeer Thunderboltr Cobalt drill bits are designed for extreme durability and long life in specialty applications. 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 and debris fast to keep the bit cool, while the 3-Flat Secure-GripT shank holds the bit firmly in the drill chuck. The 135? split point tip delivers a precision start and prevents walking for fast, accurate holes. Effective for drilling on curved surfaces, Milwaukee Thunderbolt Cobalt bits require less effort to drill through stainless steel, high alloy steel and cast iron, and are highly recommended for use with portable drills.