Blue Spot 20518 HSS Spiral Flute Step Drill (4-20mm) Features and Benefits: Ideal for precision drilling in aluminium, brass, copper, plastic, steel and wood. The spiral flute 118 degree design allows for smoother drilling, better waste disposal and improved performance when drilling harder materials. Drills holes in 2mm increments from 4-20mm. Manufactured from high speed steel for increased durability and cutting power.