Retaining rails with which a slide-in module can be fixed in a mounting cradle. It being possible for the retaining rails to be attached laterally to the slide-in module. Accordingly, the retaining rails are characterized in that they have a plastic element and a metal element. The metal element encloses at least certain portions of the plastic element, and in that the metal element has resilient retaining elements for interaction with guiding elements of the mounting cradle and in that the plastic element has resilient portions for establishing lateral tolerance compensation with respect to the sidewalls of the mounting cradle.