A kit for a helicopter , said helicopter comprising a fuselage and a rotor ; said kit 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 , in turn, comprises: - a pair of first threaded elements (21a, 21b; 20a, 20b) movable parallel along a first axis (B) and adapted to vibrate parallel to said first axis (B); - a pair of second threaded elements (20a, 20b; 21a, 21b) rotatable about said first axis (B) and operatively connected to respective said first threaded elements (21a, 21b; 20a, 20b), so as to, in use, rotationally vibrate about said first axis (B); - 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 ; said first rollers being rotatable about respective second axes (C) parallel to and separate from said first axis (B) with respect to said first female screw and first screw , and being rotatable about said first axis (B) with respect to said first female screw and first screw ; 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 ; said second rollers being rotatable about respective second axes (C) parallel to and separate from said first axis (B) with respect to said second female screw and second screw , and being rotatable about said first axis (B) with respect to said second female screw and second screw ; said first and second female screws defining said first threaded elements (21a, 21b; 20a, 20b), and said first and second screws defining said second threaded elements (20a, 20b; 21a, 21b); or said first and second screws defining said first threaded elements (21a, 21b; 20a, 20b) and said first and second female screws 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 (B) and adapted to vibrate parallel to said first axis (B); - a pair of second threaded elements (20a, 20b; 21a, 21b) rotatable about said first axis (B) and operatively connected to respective said first threaded elements (21a, 21b; 20a, 20b), so as to, in use, rotationally vibrate about said first axis (B); - 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 ; - 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 ; said second rollers being rotatable about respective second axes (C) parallel to and separate from said first axis (B) with respect to said second female screw and second screw , and being rotatable about said first axis (B) with respect to said second female screw and second screw ; <EOS>