pattern of the roll can be modified by simply rotating the insert element 12 the constructional example shown in fig1 to fig1 corresponds as regards the guiding of the pressure fluids substantially to the constructional example which was shown in fig4 and fig5 however the partition walls 5 1 and 5 2 can be displaced from the outside the partition wall 5 1 is secured to two tubes 16 1 which run in sealing tight fashion through the cover 8 of the supporting member 3 the partition wall 5 2 is secured to two tubes 16 2 which run in sealing tight manner through the partition wall 5 1 and in sealing tight manner through the cover 8 of the supporting member 3 the tubes 16 1 advantageously are all of the same length corresponding to the width of the roll so that the partition walls 5 1 and 5 2 can be adjusted over the entire width of the roll and the ends of the tubes 16 1 and 16 2 projecting from the roll give a representation of the position of the partition walls 5 1 and 5 2 finally the ends of the tubes 16 1 and 16 2 are connected by means of mobile flexible tubes to a pressure medium source 17 in the constructional example shown in fig1 an insert element 12 is arranged in the supporting member 3 and comprises helical partition walls 5 1 and 5 2.