fig4 to obtain double yarns to this end it suffices to supply in parallel two elementary yarns 3 inside the false twist spindle 7 and to deliver fibres on each of these yarns 3 for example by means of a rotary guide 10 comprising two peripheral grooves 15 each being subjected to internal suction or reduced pressure the assembly of the two core yarns obtained is effected by a simple joining guide 19 the assembled yarn being delivered to the winding means 9 by a common delivery device 8 it may also be envisaged to adapt this technique to obtaining self twisted yarns by providing downstream of the rotary guide a conventional system enabling an alternate twist to be communicated by providing the self twist in conventional manner an installation of the type illustrated in fig4 may be used for example with an intermittent delivery device being disposed between the rotary guides 10 and the false twist spindle 7 on an installation as illustrated in fig1 and 3 a core yarn according to the invention is made under the following conditions intake speed of the core yarn 3 delivery devices 4 and 6 200 m min false twist spindle 7 spindle with crossed.