Abstract: In order to obtain a lengthening maneuver of the active ends emerging from the rotating housing (1, 5, 3) containing the bobbin or bobbins (16) of the cords (F) during the rotation of said housing, the bobbin (16) has in the wall (18) of the internal hole two series of mutually staggered teeth (20, 22; 120, 122), some (20; 120) of which are developed along one axial section and the others (22; 122) along the remaining axial section; an element (34, 30), which is capable of axial sliding movements, has a disk (30) which projects elastically below the housing (1, 5, 3) and is capable of being made to reenter by means of pressure on the ground, as well as entrainment teeth (36) which are axially slidable, rotationally engaged on said housing and capable of engaging alternately the teeth of the two series (20, 22; 120, 122) upon each axial stroke and thus of permitting each time a unitary angular advance in two stages.