Adapter for inserting a sample container in a centrifuge bucket, comprising a bucket-like base body, which delimits a cavity for accommodating the sample container and has a bottom region and an adjoining side wall region, the top edge of which defines an opening edge of the cavity, and an insertion opening, through which the sample container can be inserted in the cavity and which is delimited by the opening edge, at least one separation joint being present in the side wall region of the base body, which separation joint extends from the opening edge in the direction towards the bottom region and which allows for expanding the side wall region from a starting position (P1) to an expanded position (P2) by applying a force in such a way that the opening edge has a larger circumference as compared to the starting position (P1). The side wall area has two edge regions separated from each other by the separation joint, which at least in the starting position (P1) lie one above the other radially and overlap in the circumferential direction (U), thus forming an overlap region.