A 3-fluted slot drill gives you more control when cutting than a 2-fluted one. The extra cutting edge also allows the cutter to be used at a slower speed and, as this is a carbide cutter, it stays sharper for longer. Depending on the material, coolant is essential for quality of cut and life of cutter. This set contains 3, 4, 5, 6, 8 and 10mm cutters in a twist top plastic case. Tolerances to DIN7160 and 7161.