10 and an extensible rod 13 forming a whole together between the l section 10 and the guide ruler 11 a u shaped guide channel for a rapier rod is formed a cross section of the channel for such a rapier rod 14 is only represented in fig3 the rod 13 is slidable in a separate channel 29 and carries a support 30 at its extremity to support a rapier head and to guide the rapier rod the guide unit 9 is attached to the drive casing 3 in such a manner that the distance between the centerline of the drive shaft 2 and the u shaped guide channel is adjustable to that effect the l shaped section 10 is provided with an fastening fork having two parallel legs 15 16 extending at right angles to the longitudinal direction of the l section on both sides of the drive casing 3 and are resting on the horizontal supporting surfaces 6 7 of the collars 4 5 mentioned above in order to adjust the distance between the centerline of the drive shaft 2 and the guide channel the legs 15 16 may be slid over the said supporting surfaces 6 7 the l shaped section 10 extends over the full length of the rapier rod when this rod has been withdrawn completely from the shed the l section 10 is preferably made of one piece has an l shaped section at one side and.