Fastening unit and modules

The invention relates to a fastening unit (100), in particular a fastening unit for modules which are intended to supply a user of a breathing mask or breathing hood with breathable air, and to such modules. The fastening unit is characterised in that it is designed to secure one module relative to another module, and in that it has a first component part (1) for assembly with the other module and a second component part (2) for assembly with the module, wherein the second component part (2) is rotatable, by means of the first component part (1), about a predetermined angle relative to the first component part (1); and first and second subcomponents (10, 20) within the region of the defined angle can engage with each other in a plurality of positions.