The Beijing Institute of Metrology (BIM, China) and NIST have participated in an interlaboratory comparison, in which reference Charpy specimens of three energy levels were tested. Each laboratory tested 75 specimens supplied by the other institute, 25 per energy level, at room temperature (21 °C ± 1 °C) and using an impact machine equipped with a 2 mm striker. The results obtained show good to excellent agreement between BIM and NIST, except at the low-energy level (20 J to 25 J), where NIST data obtained using a U-type machine were significantly higher than BIM data obtained using a C-type machine. Twentyfive additional low-energy BIM specimens, tested by NIST using a C-type machine, showed excellent consistency with BIM reference data and therefore confirmed that, for low-energy specimens, the configuration of the swinging hammer may affect test results, due to the different stiffness/compliance of the two machine types. A similar, but unexpected, trend was observed for the NIST super-high-energy specimens, and will need to be explained though further investigations. Key words2 mm striker; Charpy reference specimens; C-type hammer; interlaboratory comparison; U-type hammer.ii This publication is available free of charge from: https://doi.