wound coil or bobbin 19 a reversing or return motion roller 22 which drives the cross wound bobbin 19 in unwinding direction during the thread seeking operation and a conventional thread feeder arm 23 which brings the thread from the suction nozzle 21 to the thread delivery tube 7 a thread monitor 24 has a feeler which engages or rests against the running thread just above the opening of the thread delivery tube 7 as viewed in fig2 when a thread break occurs the feeler of the monitor 24 swings downwardly about its pivot to shut off a switch suitably connected to the drive mechanism for the feed roller 8 and thereby shuts off the feeding of the fibers if a thread break is registered voltage is applied to an electromagnetic actuator 25 so that a plunger or tappet 26 which is connected with the magnetic actuator 25 is moved to the left so as to be able to act upon a switch 27 a signal is thereby given to the joining carriage 51 that a thread break must be corrected at this spindle an electromagnetic actuator 28 is carried by the joining carriage 51 voltage is applied to this magnetic actuator 28 if the joining carriage 51 has made several unsuccessful joining attempts at the respective spindle and further.