A method of joining a functional module comprises the steps of providing a frame structure that defines a bearing channel with at least one circumferentially closed bearing seat; providing at least two attachment parts; providing a hollow shaft that comprises at least one support section for the at least two attachment parts, wherein the attachment parts comprise a mounting seat that is adapted to a support section; feeding the attachment parts in the bearing channel in a first feeding direction; feeding the hollow shaft in the bearing channel in a second feeding direction, wherein the hollow shaft is inserted into the respective mounting seat of the at least two attachment parts; and, subsequent to the feeding of the attachment parts and the hollow shaft in the bearing channel, at least sectionally widening the hollow shaft for a torsionally rigid fixation of the at least two attachment parts with their mounting seats at the respective support section of the hollow shaft.