A retainer for an adjustment device for an over-center fastener for securing and clamping two parts (11, 12) together by applying a pulling force between the parts by a lever (14). The adjustment device includes an externally threaded member (17a) and an internally threaded member (19) rotatable relative to one another. The internally threaded member has a friction increasing insert (24) preventing unintentional relative rotation between the externally threaded member and the internally threaded member.