Abstract: A device in back spot facing tools of the kind comprising a spindle (11), at one front end portion (12) of which, at least one wing (14) is arranged in a recess (13) and pivotally mounted parallel with and eccentrically with respect to the spindle about an axle (15, 16). The wing is at the rotation of the spindle arranged to pivot from an inactive position within the circumference of the spindle to an active position outside it. It is at the part of the wing located outside of the spindle provided with at least one cutting edge and/or a cutter (17). The pivoted part of the wing (14) outside the spindle (12) is at least at its one preferably its front end surface (21) designed with an inclined ramp (22), which in the extended position of the wing, has its maximum height, as seen in the axial direction of the wing, in a portion located closest to the circumference of the spindle (12) and is arranged to incline towards the external, curved envelope surface (23 ) of the wing.