same reference numerals as before and will not be specially described in the embodiment of fig8 one sees that the segment 14 9 has dovetail like guides 48 at its outer side with these guides engaging into complementary dovetail like openings 50 in the saw tooth strips 41 and thus securing the saw tooth strips in form locked manner to the segment this embodiment has the special advantage that individual saw tooth strips on individual segments are interchangeable in the embodiment of fig9 the saw tooth strips themselves form the segments for this purpose they are made somewhat deeper than previously in the radial dimension and provided with throughgoing holes 52 the matching drum structure is constructed as a bird cage with the individual cage bars extending through the holes 52 the exchanging of the saw tooth strips is possible here by pulling the bars out regionally and removing the corresponding saw tooth strips as an alternative to the this the base structure can have the form of a drum with a plurality of radially outwardly projecting flanges with grooves into which the saw tooth strips are inserted being provided between the ring like flanges these flanges also have bores corresponding to the bores 52 so that the bars can pass both through the saw tooth strips and also through the flanges a mounting of this kind is particularly suitable for a cylinder roller.