A fastening unit, 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 designed to secure one module relative to another module, and has a first component part for assembly with the other module and a second component part for assembly with the module. The second component part is rotatable, by means of the first component part, about a predetermined angle relative to the first component part; and first and second subcomponents within the region of the defined angle can engage with each other in a plurality of positions.