An assembly include a door trim panel including an interior surface and a tower projecting from the interior surface. The tower includes an opening accessible by a slot, an attachment feature including a flexible arm, and a rib. The rib is integrally molded to a surface of the flexible arm to define a single unitary component. A fastener has a first base, a second base, a stem located between the first base and the second base, and a head. The stem of the fastener is located in the opening, the second base is retained by the attachment feature, and the first base and the head of the fastener are located outside the tower.