clamping device 3 is guided so as to be movable on two guide rods 15 mounted to a beam 16 such that they are inclined towards the stitch forming point of sewing machine 5 clamping device 3 can be moved along guide rods 15 by means of a pneumatic cylinder 17 mounted to beam 16 and having a piston rod 18 attached to bearing part 11 the beam 16 is fastened to a traveling sleeve or carriage 19 guided so as to be movable lengthwise on a slide rod 20 fastened to frame 2 a beam 21 for a clamping device 22 fig1 and 2 is fastened to the other end of the traveling sleeve 19 and it operates like pincers in the manner of the clamping device 3 clamping device 22 comprises two arms 23 and 24 fig2 each fastened to a separate shaft 25 both of the arms 23 and 24 are rotatably mounted in the beam 21 and support a respective lever 26 and 27 at their free end and each are provided with a respective longitudinal slot 26 39 and 27 39 a double acting pneumatic cylinder 28 mounted to the beam 21 serves to open and close the clamping device 22 in that the pneumatic cylinder 39 s piston rod 29 is connected to the levers 26 and 27 by means of a bolt 30 going through the longitudinal slots.