Rivets are mechanical fasteners that consist of a smooth cylindrical shaft with a head on one end and a tail at the opposite end. On the installation, a riveter places a rivet in a pre-drilled hole, and the tail is set or bucked (i.e., deformed) with a rivet gun, rivet tool or pneumatic hammer so that it expands to about 1.5 - 2 times the original shaft diameter, holding the rivet in place. They are used to permanently join two steel, aluminium or copper plates usually in mechanical applications where it is imperative that joints do not become loose and cause failure.