For general purpose drilling in both metal & wood, these drill bits have a phosphor black finish, reduced Shank s & an overall length of 165 mm. (6-in). For use in bench & power drills equipped with 13 mm. chucks & variable speed which avoids overheating. It is always best to use a cutting lubricant when drilling metal. Bit Diameter. 20 mm. Overall Length. 165 mm.