Clearance hole for self-piercing rivet

A system for attaching layers of material together comprising:

• a self-piercing rivet having a head, body and tail;
• a plurality of layers, including:
• a top layer;
• a bottom layer free of a clearance hole and into which said self-piercing rivet is at least partially inserted;
• two or more middle layers provided between the top layer and bottom layer;
• and
• a clearance hole through which said self-piercing rivet passes during assembly in one of the:
• i) top layer;
• ii) the top layer and an uppermost layer of the two or more middle layers;
• iii) the top layer and a lowermost layer of the two or more middle layers;
• and iii) two or more of the two or more middle layers,
• wherein each clearance hole is configured to provide a hollow clearance space between the self-piercing rivet and each of the plurality of layers in which a clearance hole is provided after the plurality of layers are attached together by said self-piercing rivet with a portion of a layer of the plurality of layers in which a clearance hole is not provided being captured within the body of the rivet as the rivet pierces such layer.