Abstract: The device comprises a body longitudinally provided with a stem which is suitable for being inserted into the hole of a part being machined. On the body an element is slideably coupled which has an element for attachment to the mandrel of the machine tool, which element is adapted for imparting rotation to the body itself. On the stem is slideably mounted a shaft which is articulated at its end with a tool and is coupled to the attachment element so that an axial sliding of the same element towards the part being machined actuates a sliding motion in the opposite direction of the shaft adapted for actuating the radial projection of said tool from said stem.