Abstract: The invention relates to an apparatus for the automatic mechanical centering and simultaneous clamping of elongate round bodies of various diameter. It consists of two collet chunks arranged at an axial distance from each other in the plane of symmetry of which lies the centering axis. The two chunk arms of each collet chunk include collet jaws each of which is provided with one slide element and one grip element. The effective flanks of the grip elements are concavely curved such that they in each case engage the circumference of the round bodies when the round bodies, sliding along the effective flanks on the slide elements, have been raised by the latter until their longitudinal axes coincide with the centering axis.