Cobalt drill bits: Classic 5% Cobalt M35 High Speed Steel construction with Titanium Coating for proven capability and durability. | Hardness: 5% Cobalt drill bits’ Rock wall Hardness Level HRC 65-66. | Package & Size: 10 Pieces drill bits in a plastic bag, Diameter 17/64 inch, Total length 4-1/8 inch, Working length 2-7/8 inch. | Professional & DIY Use: For use on metal, wood & plastics, Stainless Steel, Not For Use On Concrete / Masonry. Perfect match for workshop or service vehicles. | 135 Tip & Twist Design: Increases cutting speed with self-centering and prevents walking, clears chips and particles faster.