Specification: Product name: M35 Cobalt Twist Drill Bits Set; Material: HSS-Co M35 Cobalt; Size (optional): 13PCS:1.5, 2.0, 2.5, 3.0, 3.2, 3.5, 4.0, 4.5, 4.8, 5.0, 5.5, 6.0, 6.5 mm; 19PCS:1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0mm; 25PCS:1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0mm; Measurement System: Metric; Shank Type: Straight Shank; Quantity: 13/19/25PCS + Plastic Case; Note: Cobalt drill bits require slow RPM when drilling metals. The suggested RPM is only for your reference. It may vary from different materials. You can start from a lower RPM and adjust it higher slowly. Once the bit can get into the workpiece. the adjustment should be stopped. Features: -M35 cobalt. 5% cobalt added for higher hardness and heat-resitance. The Rockwell hardness is up to 67. It can cut faster and has a long life, up to 12 times compared with the average HSS bit; -Self centering. The guiding separation point of 135 rapid cutting is self centering, which can penetrate quickly with less pressure. The straight handle can be firmly fixed and accurately centered, which is suitable for standard bit chuck and conventional round chuck; -Efficient drilling without walking. Remove chips and particleseasier and faster; -The lowest cost per hole drilled. Solid cobalt steel drill bit body can be resharpened; -Split point. Drill directly to the size needed without pre-drilling; -Fully ground. Heavy-duty fully ground body construction for minimal burr and accurate diameter; -Bits for metal. Suitable for drilling non-heat treated metals, of which the hardness is less than HRC38, such as stainless steel, copper cast iron, galvanized pipe, iron, and aluminum alloy. Not suitable for hardened steel / high carbon steel. If penetration is not possible, try adjusting the speed. Package included:(Optional) 13 PCs x Drillpro M35 Cobalt Drill Bit Set +1 PC x Plastic Case; or 19 PCs x Drillpro M35 Cobalt Drill Bit Set + 1 PC x Plastic Case; or 25 PCs x Drillpro M35 Cobalt Drill Bit Set1 + PC x Plastic Case