driven part 15 such as a tool gearbox or connecting shaft the device 10 includes a longitudinal bore 20 spanning from the end 13 to the end 14 thus providing a channel for passage of wires and other instrumentation as well known in the art and discussed above the device 10 includes a slot 32 cut through the wall 22 of the shaft 10 so as to form a serpentine path which extends generally along the path of a spiral around the shaft 10 as shown in zublin u s pat no 2 515 365 as dotted line 20 fig1 when employing the flexible shaft 10 for the transmission of power from the driven end 14 to the driven part 15 the serpentine slot 32 along the spiral path permits the device 10 to bend along the longitudinal axis of the device 10 the dovetail configuration of the serpentine slot 32 is composed of teeth 36 and 38 teeth 36 and 38 will effectively interlock the sections of the dovetail 34 above and below the teeth 36 and 38 and will thereby transmit torque where the device is to be used as a flexible shaft for power transmission the shaft typically has a diameter less than an inch but may be larger depending upon the specific application the slot characteristics shown in u s pat no 2 515 365 cannot be applied to this application a one inch or less shaft must have a lower helix angle of the helical path a higher spiral frequency and fewer cycles of slot undulations about the helical path to provide the required combination of structural strength and flexibility advantageously the slot is cut perpendicular to a plane tangent.