Abstract: A cutting insert for a cutting or breaking tool, which can be mounted in a tool holder that can be rotated about its longitudinal axis, especially for a lathe chisel, has an essentially conical tip, a transition region and a foot for connecting to a tool body, wherein the transition region has several spatial areas which are distributed over its periphery and adjoin one another forming spatial and cutting edges.

Abstract: The present invention provides a roller bit for tunnel-driving machines. Pursuant to the invention, a cutting ring has at least two or more segments. Accordingly, it is possible to renew the cutting ring itself or different parts of the cutting ring segment by segment, without the previously required dismantling and installation of a complete roller bit from a drill head and associated expenses of transporting. A total driving time is thus reduced because of shorter repair times. The segments of the cutting ring are disposed in a fixed position preferably by means of profiled guides on the base roller body and connected with the base roller body by means of segment holding devices which have a screw thread, and/or by means of threaded rings.

Abstract: A chisel holder is connected exchangeably in a fixed manner to at least one base mount disposed on a surface of a cylindrical cutting device, such as a cutting machine or a line milling machine, in a manner obviating use of a threaded setscrew. A borehole extends through the base mount, and a securing bolt received therein grips at least regionally through or behind an aligned recess formed in the chisel holder. The securing bolt is then clamped or locked to the base mount without use of threads.