against the end of the slide against the housing 19 the solenoid 20 is connected by means of a cable 25 with a thread regulator and sensing means assigned to the thread emerging from the draw frame the thread regulator emitting a pulse if the thread is ruptured which excites the solenoid 20 upon excitation of the solenoid core 21 is drawn inwardly and the bolt 22 releases the locking catch 23 and the slide 18 is caused to move by the spring 24 to the left as seen in fig1 two identical roving clamping members 26 are shown mounted on each bearing rail 13 so as to be adjustable lengthwise there along a coupling tooth 27 is secured to the slide 18 and is adapted to engage a rack 28 formed on the lower edge of the rail 13 to thereby provide a stop means which fix the clamping member adjustably to the rail 13 in this manner each clamping member 26 is conjointly movable with the slide 18 when solenoid actuated while at the same time being adjustable relative to the rail itself a locking wedge 29 is formed on the clamping member 26 so that it extends beneath the roving 12 the wedges 29 are movable into a clamping position between the paired rollers 5 5 39 and 6 6 39 respectively upon the forward movement of the rail 13 so that the roving 12 is lifted from the lower roller 5 and 6 respectively and clamped against the upper roller 5 39 and 6 39 respectively which is then held stationary by the wedge 29 a fibre tuft is produced in the area between the paired rollers 6 6 39 and the paired.