inner circumference of the tooth set ring the ring shaped clamping element 4 which is made of a flexible material is inserted into a ring shaped recess 41 of the core piece 11 the clamping element 4 possesses an inclined side 42 which operates together with projections 132 of the holder upon the installation of the holder 13 the said projections 132 penetrate into the clamping element 4 in such a manner that it is expanded radially and lies against the inner circumference of the tooth set ring 12 thus fixing ring 12 in relation to the core piece 11 and further in such a way that a slip rotation of the tooth set ring 12 is prevented the projections 132 have even a beveling for this purpose so that they can more easily press into the clamping element these can also be so formed that they are not comprised of several single projections but are connected with one another in a circumferential manner so that they form a cup shaped continuous rim on the holder 13 thus the fastening means 112 serves the ring shaped recess 41 for the purpose of binding together the core piece 11 of the opening roll 1 with the exchangeable tooth set carrier 12 the core piece 11 possesses also favorably fastening means 112 which is designed as a boring and a further fastener 41 designed as a recess so that with the same core piece 11 can work together with either a ring shaped tooth set carrier 12 or a tooth set carrier built integrally as one.