Harlingen 6 Piece Helical Cobalt M6.3-M20.5 Countersink Set Three different convex cutting edges in combination with three unequal helix angles enable extremely stable and low-vibration cutting processes without any chatter marks. Three different curved edges result in extremely stable and chatterless burr-free operation. The high grade HSS Co5 substrates hold up well in high-temperature applications, providing long tool life in a wide variety of materials. The revolutionary flute geometry and high grade substrates provide longer service life and faster countersinking. Set Includes 1 each of sizes 6.3mm, 8.3mm, 10.4mm, 12.4mm, 16.5mm & 20.5mm. This set also includes a fitted plastic case.