measuring roller 20 or 20 39 and a pressure roller 21 or 21 39 the measuring rollers 20 and 20 39 are mounted on a common driving shaft 22 and during operation rotate constantly in the direction indicated by an arrow each pressure roller 21 21 39 is mounted by way of a shaft 23 23 39 to be freely rotatable in the fork shaped end 24 24 39 of a two arm lever 25 25 39 each lever 25 25 39 is mounted substantially at its central portion on a stationary pivot pin 26 26 39 the other end of each lever 25 25 39 is connected pivotably to an operating lever 27 27 39 which can be controlled by the program setter means 18 by way of a connection 19 and a control mechanism two pairs of guide eyelets 28 and 28 39 in each case for the weft threads s 1 s 2 s 3 and s 4 are arranged on the central portion of the levers 25 25 39 mounted on the pivot pin 26 26 39 the periphery of the measuring rollers 20 20 39 and of the pressure rollers 21 21 39 consists in each case of two first and second conical peripheral portions which are inclined relatively to one another 29 30 and 31 32 on the one hand.