Drills type C-L group 0-1-2
in HSS hardness 63 HRC from Ø 4,2 to Ø 25.
You can fit them in all the Polledri mandrels of the same group.
Fitting them in the counterbores and countersinks you can to drill and to counterbore or to countersink simultaneous.
Using a good soluble oil you can increase the speed, with an increase of the tool life.