DURABLE: These countersink bits have a titanium nitride coating, meaning they last longer than regular steel countersink bits. VERSATILE: With an effective 5 flute, 115° countersink design, these 6mm (0.25") diameter shanks can be used on wood, plastic and most ferrous/non-ferrous metals. INCLUDES: The set includes sizes 8, 10, 12, 16 and 19mm.