| 1/00 | Refining of pig-iron; Cast iron |
| 1/02 | Refining of pig-iron; Cast iron Dephosphorising or desulfurising |
| 1/04 | Refining of pig-iron; Cast iron Removing impurities other than carbon, phosphorus, or sulfur |
| 1/06 | Refining of pig-iron; Cast iron Constructional features of mixers for pig-iron |
| 1/08 | Refining of pig-iron; Cast iron Manufacture of cast-iron |
| 1/10 | Refining of pig-iron; Cast iron Making spheroidal graphite cast-iron |
| 3/00 | Manufacture of wrought-iron or wrought-steel |
| 5/00 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel |
| 5/02 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel Crucible furnace processes |
| 5/04 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel Manufacture of hearth-furnace steel, e.g. Siemens-Martin steel |
| 5/06 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel Manufacture of hearth-furnace steel, e.g. Siemens-Martin steel Processes yielding slags of special composition |
| 5/28 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel Manufacture of steel in the converter |
| 5/30 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel Manufacture of steel in the converter Regulating or controlling the blowing |
| 5/32 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel Manufacture of steel in the converter Regulating or controlling the blowing Blowing from above (C21C 5/35 takes precedence) |
| 5/34 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel Manufacture of steel in the converter Regulating or controlling the blowing Blowing through the bath (C21C 5/35 takes precedence) |
| 5/35 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel Manufacture of steel in the converter Regulating or controlling the blowing Blowing from above and through the bath |
| 5/36 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel Manufacture of steel in the converter Processes yielding slags of special composition |
| 5/38 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel Manufacture of steel in the converter Removal of waste gases or dust |
| 5/40 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel Manufacture of steel in the converter Removal of waste gases or dust Offtakes or separating apparatus for converter waste gases or dust |
| 5/42 | Manufacture of carbon steel, e.g. plain mild steel, medium carbon steel, or cast-steel Manufacture of steel in the converter Constructional features of converters |