GUIDE DEVICE FOR A HOLE SAW, comprising: - a central rod; - a pair of pins threaded onto said central rod; - a plurality of arms; wherein the arms being parts of a pair are arranged substantially radially aligned with respect to the central rod; the guide device further comprising a plurality of guide bars of the same number as the plurality of pairs of arms; characterised in that the plurality of guide bars comprises at least one slot, at which the further ends of the pairs of arms are hinged; in that the arms are arranged with an X-shaped configuration; in that the pair of pins is retained onto said central rod by means of a coupling adapted to allow the variation of their mutual distance; in that the plurality of arms is arranged in pairs; and in that one of the ends of an arm that composes the pair is hinged to one of said pins, whereas one of the ends of the other arm is hinged to the other of said pins. - a central rod; - a pair of pins threaded onto said central rod; - a plurality of arms; wherein the arms being parts of a pair are arranged substantially radially aligned with respect to the central rod; the guide device further comprising a plurality of guide bars of the same number as the plurality of pairs of arms; characterised in that the plurality of guide bars comprises at least one slot, at which the further ends of the pairs of arms are hinged; in that the arms are arranged with an X-shaped configuration; in that the pair of pins is retained onto said central rod by means of a coupling adapted to allow the variation of their mutual distance; in that the plurality of arms is arranged in pairs; and in that one of the ends of an arm that composes the pair is hinged to one of said pins, whereas one of the ends of the other arm is hinged to the other of said pins. wherein the arms being parts of a pair are arranged substantially radially aligned with respect to the central rod; the guide device further comprising a plurality of guide bars of the same number as the plurality of pairs of arms; characterised in that the plurality of guide bars comprises at least one slot, at which the further ends of the pairs of arms are hinged; in that the arms are arranged with an X-shaped configuration; in that the pair of pins is retained onto said central rod by means of a coupling adapted to allow the variation of their mutual distance; in that the plurality of arms is arranged in pairs; and in that one of the ends of an arm that composes the pair is hinged to one of said pins, whereas one of the ends of the other arm is hinged to the other of said pins. a plurality of guide bars of the same number as the plurality of pairs of arms; characterised in that the plurality of guide bars comprises at least one slot, at which the further ends of the pairs of arms are hinged; in that the arms are arranged with an X-shaped configuration; in that the pair of pins is retained onto said central rod by means of a coupling adapted to allow the variation of their mutual distance; in that the plurality of arms is arranged in pairs; and in that one of the ends of an arm that composes the pair is hinged to one of said pins, whereas one of the ends of the other arm is hinged to the other of said pins.