Dormer A100 HSS Jobber Drill Bit Number Size N4 Pack of 10

Series A100 HSS Straight Shank Jobber Drills - Gauge Suitable for drilling steel, cast steel, alloyed and unalloyed, grey cast iron, spheroidal iron, sintered powder metal, German silver and graphite. Manufactured to BS328/DIN338RN. Black Finish (W-Finish) This is the most common surface finish and is the result of a steam tempering operation in which steam is passed over the product during a controlled tempering cycle, producing a black oxide layer. Black tools are generally recommended for ferrous applications where the oxide layer aids chip flow, helps to dissipate heat by retaining some coolant on the tool surface and also helps to prevent the tool from staining.