A fastener with critical configuration of the barbs, which allow the extraction of the fastener without destruction of the slot and/or the fastener. This critical configuration of the barbs allows fasteners to be used in slots of various widths and prevents rattling, which would take place in the case of fasteners of the present state of the art. The critical configuration is based on the special dimensions and special shape of the barbs with regard to the parts and the slots involved in assemblies of the fasteners and the parts. Assemblies of miscellaneous parts connected together by means of such fasteners, as well as vehicles comprising such assemblies may be made. In addition, fasteners with a combination of low and high barbs, which combination prevents rattling of the fastener and allows secure attachment on a part, such as a sheet metal, for example, are included.