disclosed the device comprises a tensioning means of any type a drive member whose rotation results in the movement of the tension generating member of the tensioning means a feeler element over which the thread passes and which is moved when the length of thread absorbed and or the tension of the thread varies and two switches one controlling the placing in rotation of the drive member in one direction and the other the placing in rotation in the other direction the direction of rotation of the drive member is selected so that the corelative action of the feeler corrects the variation in the length of thread absorbed and or of the tension which is the cause of triggering this rotation application_number US 53677083 A description the thread 2 supplying the flat knitting machine of which only the needles 16 are shown is paid out from its spool 1 by alternate movements of the carriage of the machine actuating the thread take up by the needles 16 in the embodiment illustrated by fig1 the thread 2 passes over the fingers 17 and 18 of the tensioner 3 so as to form a barrage means before passing over the thread guide 5 the two fingers 17 and 18 are fixed to one of the flat surfaces of a cylindrical support 20 symetrically with respect to the axle 19 of said support the rotation of the cylindrical support causes the contact arc of the thread with the two fingers of the barrage means to vary and therefore to vary.