Abstract: The device comprises a series of tool carriers each of which is provided with a tool, a connector tang and aseries of three abutments disposed substantially around the axis of the tool and in a plane orthogonal to the axis itself, a rack provided with a plurality of seats each of which is able to support a tool carrier, a support unit fixed to the head of the machine is provided with a series of frontal surfaces operable to constitute bearings for the said abutments; this unit is provided with connector means operable to grip the connector tang of one of the tools, and displacement means operable to support the connector means and to displace it with respect to the support unit in the direction of the axis of the tool from a first position in which the abutments of the said series of abutments are at a predetermined distance from the frontal surface of the first defined series, to a second position in which the abutments themselves are in contact with the frontal surfaces, the displacement from the first to t