Jobber Drill - Black | Metric (BULK) 1.00 - 7.9mmBlack Finish Jobber Drills (also called blue finish) achieve their distinctive colour by steam tempering, a thermal process resulting in a porous tool coating. This surface helps to keep lubricant on the tool, particularly important on the cutting edges, thus reducing friction and cold welding. The result is increased tool life. Black finish tools are generally recommended for ferrous applications where the oxide layer aids chip flow and heat