Fasteners characterized by structures which are suitable to be engaged reversibly in a slot of a rigid part, such as a metal sheet or the frame of a car for example. The structure provides easy insertion but difficult extraction of the fastener from the slot, without producing squeaking noises during end-use. Easy manufacturing and high dimensional accuracy are also great assets of the fasteners. The invention also pertains to an assembly of said rigid part and the fastener, an assembly connecting parts with the fastener of this invention, as well as vehicles comprising such assemblies.