Abstract: A first part of plastic material (7), preferably a component of a package, is secured to a second part (2). Tubular projections (9) are formed in the first part and are introduced through a hole (4) in the second part. The projection (9) is shaped with an outer terminating portion (11, 12) closing the same, and forming a vaulted termination extending outwardly and provided with such a crease that it can be brought to an at least somewhat inwardly bulging position. After the second part (2) with its hole (4) has been placed on the projection (9), a surface is laid against the vaulted termination and is pressed against the same, so that it is inversely forced into its inwardly bulging position. In this position it causes such a widening of the portion (10;14) of the projection located inside of the termination that this portion forms a rivet head (13;19).