Анотація: In light of the new Rockwell C hardness scale definition adopted by National Metrology Institutes (NMIs) [1], a comparison of the Hardness Rockwell and Superficial- Rockwell scales realized by National primary hardness Rockwell machines is necessary to verify the implementation of the new definition. A Technical Protocol of a Regional Metrological organization Key Comparison (RMO KC) was presented and approved at the t TC 1.6 meeting in September 2014 in Braunschweig, Germany. A Regional Key Comparison (RKC) has been chosen and the technical protocol has been prepared following the rules given by the document “Measurement comparisons in the CIPM MRA” [2].