The invention relates to an assembly unit having an assembly part, which is penetrated by a bore and is to be fastened to a basic structure. The basic structure having a shaft, a head, and a fastener. The fastener having a fastening section on the end thereof facing away from the head, which is held captively and movably in the bore between a first axial position and a second axial position. The assembly unit having a spring, which encompasses the shaft and is formed from a wound spring wire and which holds the fastener captively in the bore. The spring wire is wound in a spiral shape such that the windings thereof do not overlap in the radial direction relative to the spring axis.