Threaded shank drill bits are type D adapter style. They are made from M42 8% cobalt and are manufactured to NAS 965 Type “D” specifications. They have 135ÂÂo heavy duty split point and surface treated for drilling hard, tough, high tensile strength materials. When drilling low tensile strength materials, the Type “D” cobalt drill will have a significantly greater tool life than the NAS 965 Type B high speed steel adapter drill, resulting in a much lower cost per hole.