characteristic of the present invention lies in the fact that the two cylinders 2a and 2b are arranged with their axes horizontal and parallel but mutually offset so that the fibres are firstly compelled to pass along a spiral path about the cylinder 2a to reach a transfer region 16 between the two cylinders in which the staple fibre stream which has passed about the cylinder 2a and has been subjected to its action is passed to the subsequent cylinder 2b along a passage path of 34 spectacles 34 form according to a preferred embodiment of the present invention the cylinders are right cylinders of identical size and lie axially side by side the length of the axial portion common to the two cylinders in correspondence with the final section of the first cylinder 2a and the initial section of the second cylinder 2b with reference to the direction of movement of the material in which the fibre tufts pass from the first to the second cylinder is between 5 and 40 of the length of each cylinder the parallel axes of the two cylinders preferably lie in the same horizontal plane a further important characteristic of the present invention lies in the fact that the constituent.