A kit (1, 1') for a helicopter, said helicopter comprising a fuselage and a rotor; said kit (1, 1') comprising at least one device designed to dampen the vibrations transmitted from said rotor to said fuselage and be interposed between said fuselage and said rotor; wherein said device (15, 15'), in turn, comprises: - a pair of first threaded elements (21a, 21b; 20a, 20b) movable parallel along a first axis and adapted to vibrate parallel to said first axis; - a pair of second threaded elements (20a, 20b; 21a, 21b) rotatable about said first axis and operatively connected to respective said first threaded elements (21a, 21b; 20a, 20b), so as to, in use, rotationally vibrate about said first axis; - a first inerter; and - a second inerter; said first inerter, in turn, comprising: - a first female screw; - a first screw operatively connected to said first female screw; and - a plurality of first threaded rollers, which are screwed on said first female screw and first screw (21a, 20a); said first rollers being rotatable about respective second axes parallel to and separate from said first axis with respect to said first female screw and first screw (21a, 20a), and being rotatable about said first axis with respect to said first female screw and first screw (21a, 20a); said second inerter, in turn, comprising: - a second female screw; - a second screw operatively connected to said second female screw; and - a plurality of second threaded rollers, which are screwed on said second female screw and second screw (21b, 20b); said second rollers being rotatable about respective second axes parallel to and separate from said first axis with respect to said second female screw and second screw (21b, 20b), and being rotatable about said first axis with respect to said second female screw and second screw (21b, 20b); said first and second female screws (21a, 21b) defining said first threaded elements (21a, 21b; 20a, 20b), and said first and second screws (20b, 20a) defining said second threaded elements (20a, 20b; 21a, 21b); or said first and second screws (20b, 20a) defining said first threaded elements (21a, 21b; 20a, 20b) and said first and second female screws (21a, 21b) defining said second threaded elements (20a, 20b; 21a, 21b). - a pair of first threaded elements (21a, 21b; 20a, 20b) movable parallel along a first axis and adapted to vibrate parallel to said first axis; - a pair of second threaded elements (20a, 20b; 21a, 21b) rotatable about said first axis and operatively connected to respective said first threaded elements (21a, 21b; 20a, 20b), so as to, in use, rotationally vibrate about said first axis; - a first inerter; and - a second inerter; - a first female screw; - a first screw operatively connected to said first female screw; and - a plurality of first threaded rollers, which are screwed on said first female screw and first screw (21a, 20a); - a second female screw; - a second screw operatively connected to said second female screw; and - a plurality of second threaded rollers, which are screwed on said second female screw and second screw (21b, 20b); said second rollers being rotatable about respective second axes parallel to and separate from said first axis with respect to said second female screw and second screw (21b, 20b), and being rotatable about said first axis with respect to said second female screw and second screw (21b, 20b);