Abstract: The yarn pieces to be joined are stretched between the two pairs of suction tubes (28, 29; 30, 31) and untwisted by being wound about spindles (20, 21). Hot compressed air fed along the surface of two blocks (32, 33) adjacent to the untwisted yarn portions remove free fibers and distribute the fiber tufts in the base of a channel formed in said blocks (32, 33). Said tufts are retained in the base of the channel by an electrostatic field formed with the aid of conductors (46) and the generator (GE). The blocks are then rotated about the rotation shafts (4, 5) until the channel edges are in contact with each other. Air is fed perpendicularly to the plane containing the fiber tufts in proximity to their respective ends in order to cause the fibers of the two tufts to interpenetrate, the spindles (20, 21) then being driven in the reverse direction in order to twist the fiber tufts and to disengage the yarn.