on the left side of carrier 8 as seen in fig2 a separator blade 11 is fixedly attached to the carrier with for example two hexagon socket screws 12 non illustrated slots in separator blade 11 permit the precise positioning of the blade tip thereof with respect to the saw tooth clothing of roller 1 as shown in fig2 carrier 8 is also at least in the area adjacent to end cap 6 prismatically arranged via which the precise positioning of the carrier 8 with respect to end cap 6 occurs automatically as shown in fig2 end cap 6 is a unitary part of axle box 4 thereby forming an extension of the axle box which is generally made of cast iron which spaces the working element from the carding or working element 7 by a predeterminate precise amount however as shown in fig3 end cap 6 may alternatively be a separate part which is fixedly attached such as by screws to axle box 4 this latter embodiment however has the disadvantage that in this manner a less precise control of the positioning of the working elements with respect to the rollers is achieved since the attached connection also adds further tolerances by means of abutting engagement surfaces the apparatus of the invention provides for precise distance positioning and centering positioning or in other words.