Abstract: Drilling/chamfering tool, comprising a tool holder (3) which holds at its front end a chamfering head (2) and a commercially available drill (1) with cylinder shaft, and appropriate adjusting and cutting elements. It is essential in the drilling/chamfering tool that the cylinder shaft (D) of the drill (1) is greater than or equal to the drill diameter (g) and has at least one clamping surface (g). The chamfering head (2) is rotatable 360.degree. about the tool axis (a), while two chamfer cutting blades (4) are arranged diagonally opposite each other in the chamfering head (2) and are clamped adjustably against the diameter (d.sub.1) of the spiral back (j) essentially at chamfer angle (.lambda.). The particular advantage is obtained that optimum cooling and no accumulation of chips is achieved and a modular tool system with uncomplicated availability and inexpensive procurement and storage is provided.