High-performance flat countersinks made from HSS according to DIN 373 for countersinking cylinder head and hexagon screws as well as nuts. Flat countersinks have a cylindrical design. The cylindrical pin in the relevant quality grades of fine, medium or tapping hole ensures coaxial alignment of the countersink to the bore. High-performance countersink tools for through holes with the quality grade fine (F) according to ISO 273.