Abstract: An assembly device for permanently joining at least two parts includes a rivet element having a head and a rod formed of a material which is deformable by compression, and a washer having an opening through which the rod extends when the rivet element is assembled to the parts to be joined with the head abutting one of the parts and the rod extending through the parts. A volume of the opening in the washer is at least equal to the volume of the rod projecting from the parts to be joined when the rivet element is asembled thereto. Assembly while maintaining a degree of freedom between the parts to be joined can be provided by selecting the rivet elements so that the height of its section closest to the rivet head is at least equal to the thickness of the part being joined which is abutted by the head.