A screw mechanism, comprising a first and a second screw (1, 2), which each have a head end (11, 21) and an opposite foot end (12, 22), wherein a respective screw (1, 2) in the region of the head end (11, 21) can be connected to another part of a device which includes the screw mechanism, and of which the first screw has a threaded portion with a right-hand thread and the second screw has a threaded portion with a left-hand thread, and a common nut which has a passage opening, the wall of which is provided with a first mating thread for the first screw and a second mating thread for the second screw, wherein the first and second screw can be screwed into the mating thread (5, 6) of the nut from opposite sides of the nut, characterised in that the threaded portions (13, 23) of the first and second screw (1, 2) each have at least two partial portions (13a, 13b; 23a, 23b), the outer surfaces of which form peripheral parts of circular-cylinder circumferential surfaces which are provided with the right-hand or left-hand thread (15, 25), at least one of the screws (1, 2) having in the region of its longitudinal centre line (17, 27) a slot (16, 26) starting from its foot end (12, 22), which slot separates the partial portions (13a, 13b; 23a, 23b) at least over a portion of their axial extent, the first and second screws (1, 2) directed towards each other with their foot ends (12, 22) being able to be inserted axially into one another, in that the first and second mating thread (5, 6) of the nut, at least over a portion of their axial extents, are introduced into the same axial portion of the wall of the passage opening, lying one in another, in that the first and second mating thread (5, 6) are introduced over at least two thirds of their axial extent into the same axial portion of the wall of the passage opening, lying one in another, and in that the first and second screws (1, 2) can be inserted axially into one another over at least two thirds of the axial extents of the threaded portions (13, 23) of the first and second screws (1, 2). a first and a second screw (1, 2), which each have a head end (11, 21) and an opposite foot end (12, 22), wherein a respective screw (1, 2) in the region of the head end (11, 21) can be connected to another part of a device which includes the screw mechanism, and of which the first screw has a threaded portion with a right-hand thread and the second screw has a threaded portion with a left-hand thread, and a common nut which has a passage opening, the wall of which is provided with a first mating thread for the first screw and a second mating thread for the second screw, wherein the first and second screw can be screwed into the mating thread (5, 6) of the nut from opposite sides of the nut, characterised in that the threaded portions (13, 23) of the first and second screw (1, 2) each have at least two partial portions (13a, 13b; 23a, 23b), the outer surfaces of which form peripheral parts of circular-cylinder circumferential surfaces which are provided with the right-hand or left-hand thread (15, 25), at least one of the screws (1, 2) having in the region of its longitudinal centre line (17, 27) a slot (16, 26) starting from its foot end (12, 22), which slot separates the partial portions (13a, 13b; 23a, 23b) at least over a portion of their axial extent, the first and second screws (1, 2) directed towards each other with their foot ends (12, 22) being able to be inserted axially into one another, in that the first and second mating thread (5, 6) of the nut, at least over a portion of their axial extents, are introduced into the same axial portion of the wall of the passage opening, lying one in another, in that the first and second mating thread (5, 6) are introduced over at least two thirds of their axial extent into the same axial portion of the wall of the passage opening, lying one in another, and in that the first and second screws (1, 2) can be inserted axially into one another over at least two thirds of the axial extents of the threaded portions (13, 23) of the first and second screws (1, 2).