Overview Reviews Product Description This Irwin Unibit® #1 cobalt step drill bit is engineered with m-35-grade cobalt steel for maximum life when drilling in tough steel.Laser-marked sizes enable easy reading.The radial concave flute design helps ensure an effective use of drilling power. Irwin Tools Catalog Product Videos Custom Field Manufacturing country US Product Reviews Write a Review Write a Review × Irwin UNIBIT® 1/8 - 1/2" #1 Cobalt Alloy Steel Step Drill Bit 10231CB Rating * Select Rating 1 star (worst) 2 stars 3 stars (average) 4 stars 5 stars (best) Name Review Subject * Comments *