of curved bars 51 54 the bars are curved to have a profile similar to that of the profile of the mandrel 40 and the first bar is positioned so that the profile projects in one direction transversely to the path of the fabric in this embodiment upwardly of the path of the fabric and the next curved bar 52 having a similar profile projecting in the opposite direction transversely to the path of the fabric i e downwardly from the path of the fabric the third curved bar projects in the one direction i e upwardly and the fourth curved bar projects in the other direction i e downwardly the fabric moving from the shed to the mandrel is diverted back and forth across the normal path of the fabric over each of the bars until it reaches the guidebar 44 the maximum point of projection of the contour of the bar is at the position corresponding to the center of the longitudinal length of the mandrel 40 and the lowest point on the profile of the bars corresponds to the position of the ends of the mandrel and lies along the path of the fabric it will be seen that the warp yarn or yarns which lie along the center of the fabric will be diverted by the first bar 51 out of the normal direct path from the position of the shed to the guide bar 44.