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9 gauge aluminum sheet plate refers to a specific thickness measurement of aluminum sheet metal. The gauge system is a widely used method to determine the thickness of various materials, including aluminum.

In the gauge system, a lower gauge number corresponds to a thicker material. However, it's important to note that the gauge system can vary slightly depending on the specific standard or country being used. In the United States, the gauge system used for aluminum sheets typically follows the Aluminum Association (AA) standard.