The invention relates to an assembly system including a member made of at least a first material including a staff and a shoulder, the staff of the member being received in an aperture of a part made of a second material having little or no plastic domain. According to the invention, the assembly system includes a locking element made of a third material arranged to elastically attach the part between the shoulder of said member and the locking element and in that the locking element is a washer whose internal wall radially grips the staff of said member and whose peripheral portion exerts an elastic radial force vertical to the shoulder of said member in order to secure the assembly of the member-part-locking element.