Threaded shank drills are type “D” adapter drills are made from M42 8% cobalt high speed steel are manufactured to NAS 965 Type “D” specifications with 135o heavy duty split point and surface treated for drilling hard, tough, high tensile strength materials. When drilling low 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.