a convex surface 23 the needles of the bars 17 are off set from one element to the other in the zone of co operation of the said elements in accordance with one feature of the invention the convex surface 23 of each bars 17 is of a circular cross section and of a radious such that at the passage of the chains 20 21 over the outlet wheels 11 12 the circular contour of the corresponding bars is coaxial to the said wheels in this way the outlet movement of the needles from the structure of the sliver at the end of control is effected materially without any relative movement between the needles and the sliver since the sliver unrolls from the convex surfaces 23 with reduces to its minimum the displacement of the fibres created by the exit of the needles in accordance with another feature of the invention the pair of upper return wheels 11 is set back relative to the pair of lower wheels 12 so that the upper drawing cylinder 15 of a larger diameter than the lower drawing cylinder 16 can occupy a position very close to the lower endless element 8 in this way as is shown in fig1 the distance which the drawn sliver 2a covers between the end of the control.