Abstract: In order to maintain a desired feed velocity in a glass-fiber thread passing via a traveler from a supply bobbin to a cop on a spindle, the thread is led upstream of the traveler through the nip of a pair of rollers that are set in rotation by its motion to drive a tachometer working into a speed regulator which controls the bobbin drive. The output signal of the tachometer may further be used to measure the length of thread payed out from the supply bobbin and/or to generate an alarm signal stopping the bobbin and spindle drives in the event of a slowdown of the roller rotation indicative of a thread break; such an alarm signal could also be produced when a speed sensor coupled with the bobbin drive detects an excessive increase in its operating speed caused in the event of a thread break by feedback from the tachometer.