Main textThis report describes the results of comparison COOMET.M.H-S3. The comparison measurements between the five participants NSC "IM" (pilot laboratory), PTB, CMI, BelGIM, KazInSt were started in December 2014 and ended in December 2016. In the RMO SC, one set of hardness reference blocks was used consisting of 6 (six) blocks of the Superficial-Rockwell scales and hardness levels 90-94 HR15N, 40-50 HR30N, 76-84 HR30N, 43-54 HR45N, 47-53 HR30TW, 70-82 HR30TW. Agreement between the results of the participants is good.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).