Self-piercing rivets are the most common fastening method used by the OEMs. They are specially-coated steel rivets that pierce the outer body panel and mushroom into the inner body panel without piercing it. A special coating, usually tin/zinc, prevents galvanic corrosion. A special tool is used to press the rivet into place and it must have access to both sides of the panel. Self-piercing rivets are used on aluminum body panels because they duplicate the performance of spot welds without heating the aluminum.