This IRWIN 5-Piece Left-Hand Mechanics-Length Cobalt Alloy Steel Drill Bit Set includes drill bits made of M-42 8% Cobalt Alloy Steel high-speed steel for super abrasive resistance in tough metals. The 135° split point reduces feed pressure for easier penetration without work hardening, and the heavy-duty spiral flute design produces fast chip ejection. The shorter drill bit length gives added strength and allows you to drill into fasteners without tightening them and often remove broken fasteners without an extractor.