cobalt twist
Photo: Keate
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Cobalt Twist (for stainless steel, cast iron)

Most twist bits can drill into mild steel and other thin metals, but you'll need this alloy to plow through more stubborn materials. Drilling into steel can push a bit's temperatures to 1,100 degrees; cobalt dissipates heat so efficiently that the cutting edge stays cool and sharp. $5 for the 1/4-inch shown; 1/16 to 1/2 inch;
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