Abstract: Standard metallic scales (Grade III) are the third-grade line standards in the Verification Scheme of Line Measuring Instruments and are used for calibrating rigid working line scales, such as steel rulers, in China. To ensure the consistency of the measurement values of standard metallic scales (Grade III) and to scientifically evaluate the Calibration and Measurement Capabilities (CMC) of these scales in China, the National Institute of Metrology, as the pilot laboratory, organized a national measurement comparison of standard metallic scales (Grade III) (project number 2021-B-04), with seven laboratories participating. This paper introduces the basic information, technical scheme, and results of the comparison, analyzes the existing problems in the calibration of standard metallic scales (Grade III), and provides technical suggestions. The comparison results show that the normalized deviations of all participating laboratories are less than 1, indicating satisfactory comparison results.