5PCS,5/16" Inch HSS Jobber Cobalt Twist Drill Bits,ideal for drilling on mild steel, copper, Aluminum, Zinc alloy etc. High Quality Material- High Speed Steel Cobalt -M 35 Cobalt Steel Best Material. High Efficiency In Drilling Metals, and Stainless Steel. Ideal for drilling in tough metal, including heavy-duty abrasive alloy metal drilling on hardened steel 135-degree split-point tip starts drilling immediately with less force and eliminates "walking" across the work surface