Abstract: Each of the thread guide wings comprises a pair of leg members. Teeth located at the leg members of each pair mesh with an associated gear secured to an associated concentrically arranged adjustment shaft. By accomplishing relative motion between the adjustment shafts, which carry the thread guide wings, and the associated gear it is possible to adjust the diameter or lengthwise extent of the thread guide wings by displacing the leg members. A corresponding reduction or enlargement of the diameter or lengthwise extent of the thread guide wings causes a displacement of the thread transfer points and thus the stroke along which the thread is shifted. Altering the thread stroke can be accomplished by a stepping motor or as a function of the diameter of the bobbin upon which the thread is wound.