Levi Strauss & Co. first used the 501 lot number for its riveted trousers in 1890.
The company had been making riveted work trousers since the 1873 patent, but early products were identified through descriptions and other lot references rather than the modern model name. In 1890, Levi Strauss & Co. assigned the number 501 to its signature copper-riveted waist overalls.
The number became one of the most recognizable product identifiers in clothing history. Over time, the 501 developed from workwear into a broadly worn casual garment, while its button fly, five-pocket layout, and denim construction became especially influential.
The lot number does not mean the jeans were invented in 501 or that 501 pairs were made. It was an internal product designation. The apostrophe in the informal expression “501s” is also not part of the official model name.