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.