The XX jean was the name of Levi’s 501 jeans before they were called 501. The name XX was derived from a notation used in price lists to mean “extra, extra strong,” and reflects the status of jeans as working wear. Levi’s XX jeans originally had only one back pocket, with a second back pocket added in 1901. The pants were renamed 501 in 1890 to refer to a specific lot number. In acknowledgment of these original jeans, Levi’s reintroduced the XX name in 2009.