Early Office Museum web site, unknown author, History of the Apple. Consulted on July 2, 2008.
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DE 121067C, Vaaler, Johan, "Aus Draht hergestellte, büegelföermige Klammer zum Zusammenhalten von Papierblättern u. dgl. [Iron wire eyelet clip for holding together sheets of paper and the like]", published 1901-06-06