The disclosure relates to a retainer (100) for sample carriers (P1-P4) of different shapes and sizes. The retainer includes a retaining plane (110) for receiving the sample carrier; at least three respectively movably mounted stop elements (120), each of the stop elements (120) having at least one stop surface (121) which is embodied to be adjusted, by movement of the stop element (120), against the sample carrier (P1-P4); at least three securing elements (125), a securing element (125) being associated with each of the at least three stop elements (120); each of the at least three securing elements (125) configured to secure the associated stop element (120) immovably on the retainer, and configured to be conveyable into a first position in which the associated stop element (120) is movable, and to be conveyable into a second position in which the associated stop element is secured immovably on the retainer.