The ASTM C366/C366M-16 (2022) e1 standard provides a standard test method for sandwich core thickness measurement. The standard applies to core parts in sandwich structural materials, especially composites commonly found in construction, aerospace, and Miscellaneous industrial applications. The standard details methods for sandwich core thickness measurement using different measurement tools (e.g. caliper, Micrometer, etc.), including operating specifications in the measurement process, precautions, and accuracy requirements for the measurement results. By implementing this standard, it is possible to ensure that the sandwich core material meets the specified thickness requirements during the manufacturing process, thus guaranteeing the performance and safety of the composite.