Rebar is a steel bar, which is embedded in concrete in buildings, bridges and other structures to give more strength to the structure.
Where would this be classified in ISIC, in ISIC 2511 Manufacture of structural metal products or in ISIC 2410 Manufacture of basic iron and steel?
In ISIC 4 we would put the manufcature of rebar in 2410 (Manufacture of basic iron and steel).
As these are simply steel bars, we would not consider them under structural metal products (a tied rebar beam cage would be a different story, although I doubt that this is "manufactured" outside of the construction process).
This treatment would also be consistent with the previous version of ISIC.