Abstract: An undercut anchor 2; 30, which facilitates the formation of a corresponding undercut in a blind hole for receiving the undercut anchor 2; 30, is formed to independently cut or form this undercut by rotating and spreading the undercut anchor 2; 30. Furthermore, a setting tool for forming this undercut at the bottom of the blind hole in the joining partner is proposed. Finally, a method of forming an undercut at the bottom of a blind hole using the setting tool is disclosed.