A tool and a cutting insert for chip removing machining includes a tool body with an insert seat, a cutting insert mounted in the insert seat, and a fastening member. The cutting insert includes a first locking member extending in an area located outside of a central axis of the cutting insert. A second locking member configured to engage with the first locking member is provided in the insert seat. The fastening member extends through a through-hole and bears on a lower contact region of the cutting insert to press the cutting insert against a top support member provided rotationally ahead of the insert seat so that the second and first locking members lock with each other and form a radial support for the cutting insert, and on the other hand it presses an axial support region in the side surface of the cutting insert against an axial contact surface provided in the insert seat.