Three high speed steel double flute step drills allows clog free precision drilling of eighteen different size holes with just three bits supplied in flip up metal case size 1 4 5 6 7 8 9 10 11 12mm size 2 4 6 8 10 12 14 16 18 20 22mm size 3 4 6 8 10 12 14 16 18 20 22 24 26 28 30mm