Abstract: Of application in processes of assembly by screwing between a plastic piece and a supporting base, for example a bodywork, from which a fastener stands out perpendicularly. It is constituted by a circular base and a hexagonal body traversed by a central drilled hole which passes through and has a main segment and an expansion in which are some slightly arched internal protuberances which constitute the fastening means for connection of the nut to the fastener after a slight rotation of or pressure from the former and it determines the fastening and provisional positioning of the plastic piece with respect to the supporting base prior to its screwing. During the screwing operation the cutting effect which the metal fastener applies on the plastic walls of the drilled hole gives rise to a thread.