Milwaukee's Thunderbolt Silver & Deming drill bits are designed for performance in low to high tensile strength materials, stainless steel and cast iron. Thunderbolt twist drill bits are made from premium industrial-grade steel with heavy-duty cutting surfaces that power through deep or shallow holes with lightning speed. A special flute geometry adds strength while providing increased chip ejection. Thunderbolt twist drill bits have a heavy duty 135 degree split point for easy penetration and a 1/2 in. reduced shank with 3 milled flats which prevent slippage in a jawed chuck.