A twist drill or rotary cutting device, in particular a drill, comprising a tool head or cutting insert consisting of a hard cutting material and a tool shaft which clamps the tool head between two clamp extensions that project axially from said tool shaft in such a way that the tool head is interchangeable. In the fixed position, the interconnected clamping surfaces of the tool head and the clamping extensions of the tool shaft lie on the surface of a truncated cone shaped fixing peg running coaxially with the longitudinal axis of the tool shaft. The fixing peg tapers in the insertion direction, facing the chuck end of the tool shaft.