A fastener having a grip member (1) that is insertable into a mounting space (3) of a hollow structure (2) and serves in the detachable fastening of an object to the hollow structure. The grip member (1) is rotatable inside the hollow structure such that the grip member (1) grips behind holding projections provided inwardly of the hollow body longitudinal walls. The holding projections are for fastening of the object between a stop (7), that outwardly abuts the edges of the hollow structure's longitudinal walls (4) lining the mounting space and can be fixedly clamped to the grip member (1). A spring biased element (13) acting perpendicular to the stop (7) is arranged between the grip member and the stop. The result is that pre-fixation of the fastener to the hollow structure is made possible. By means of a coupling (15) between the stop (7) and the rear grip member (1) its positions are precisely fixed.