often the case that in accordance with fig4 a to 4 d first the preliminary draft zone vv is modified and then the main draft zone hv in the case of shortening of the draft zones vv and hv the slider 36 a is displaced in the direction of the arrow e from the position according to fig4 a into the position according to fig4 b as a result the nip line spacing in the preliminary draft zone vv is reduced from u201c a u201d to u201c a u201d then in accordance with fig4 c the sliders 36 a and 35 a are rigidly connected to one another by means of a bridge 50 finally the rigidly coupled sliders 36 a and 35 a are moved in accordance with fig4 d in the direction of the arrows e and c from the position shown in fig4 c into the position shown in fig4 d as a result the nip line spacing in the main draft zone hv is shortened from u201c b u201d to u201c b u201d a corresponding procedure is used in the case of lengthening the preliminary and main draft zones that is to say the coupled sliders 35 a and 36 a are displaced in the direction of the arrows f and d see fig2 as a result of which the main draft zone hv is lengthened then the sliders 35 a and 36 a are uncoupled from the bridge 50 finally the slider 36 a is moved in the direction of the arrow f see fig2 as a result of which the preliminary draft zone vv is lengthened with regard to the fibre slivers 5 in the drawing mechanism 2 it should be noted that in.