see particularly fig1 fastening area 230 of mixer 204 is designed correspondingly housing 221 of the fastening area of the mixer is provided with the external coding means namely visual coding nose 222 coding cam 223 that fits into coding gap 212 on the cartridge and a coding segment 224 that fits between the coding rims on the mixer in fig2 the interior elements of the mixer are depicted i e the two inlets 225 and 226 the inlets having different diameters in accordance with the outlets or alternatively equal diameters the mixer housing further comprises two snap openings 227 and 228 for receiving snap noses 218 and 219 on the cartridge in contrast to the preceding exemplary embodiments the fastening area of the mixer comprises two additional retaining elements the two snap ledges 229 and 229 a whose noses are adapted to engage behind snap openings 207 and 208 on the cartridge flange in order to provide a higher retaining force than in the previous exemplary embodiments the sectional views of fig2 and 22 illustrate the forces f that are applied to the fastening area of the mixer during the withdrawal of the mixer thereby compressing the latter in the direction of the two f arrows and expanding it in the direction of the two arrows s in this manner the positions of these fig2 and 22 are reached fig2 showing a sectional view according to plane xxi xxi and fig2 a sectional view.