Irwin Tools 31520 5/16-Inch Cobalt 135-Degree, Left Handed-Mechanics Length, Pack of 6 This drill bit features 8% cobalt-alloyed steel construction for high heat- and abrasion-resistance Shorter drill bit length provides additional strength Drill bits have a heavy-duty spiral flute design that produces faster chip ejection Shorter cutting lips reduce torque for drilling in high-tensile-strength materials 135 split point reduces feed pressure for easier penetration without work-material hardening