Levi Strauss & Co.'s first riveted blue-jeans model was called XX.
The name came from the patent-era product designation used for the trousers made by Levi Strauss and Jacob Davis. Their 1873 patent covered the use of copper rivets at stress points, especially the pocket corners, making work trousers more durable.
The XX designation predates the famous 501 name. Levi Strauss & Co. later used numbered model names as its product range expanded, with 501 becoming the best-known example. This means XX should not be confused with the 501, which became an iconic later Levi's model.
The early riveted trousers were workwear rather than fashion garments. Their popularity grew among miners, laborers and other workers who needed sturdy clothing. The patented rivet construction helped distinguish them from ordinary denim trousers and established the foundation of the Levi's jeans business.