fig4 shows a holder for the monitoring of a group of five threads and for each thread to be monitored a flexible contact arm which has a thread guiding eye is held at a distance from a contact strip by the tensioned thread whereas in case the thread breaks the contact arm touches the contact strip triggers an alarm and or stops the machine the mode of operation of the device can be explained by means of fig5 s is a tensioning device for the thread f which is guided through the eye 71 of the flexible contact arm 7 the thread tension k holds the contact arm in the illustrated position the contact arm is made of steel wire and includes a torsion spring part 72 which is held at 73 on part of the sawing machine to the rail 3 and the connection 73 shared by all contact arms there is connected a control device g supplying the voltage also suitably mounted on the machine frame to the electronic control device there can also be connected a shut off device not shown which shuts off the machine with adjustable time delay a time delay is useful since because of a disturbance lasting a short time a thread can hang slack without breaking in fig1 3 1 is a holder of insulating material which is designed as a conducting plate and on whose back side conducting paths 11 13 are located the holder is clamped movable on a current carrying rail by means of a clamping part 2 a screw 21 a washer 22 and a nut 23 the conducting path 11 provides here an electrically conducting connection with the rail 3 a light diode 4 is soldered onto the conducting path.