The lexicon of the top500 ( The Encyclopedia for Classification Codes ) explains the codes and definitions in the world of economical classifications.
NAICS Code 3313 Alumina and Aluminum Production and Processing
The NAICS Code 3313 is described as
Alumina and Aluminum Production and Processing It belongs to the code group
NAICS Code 331 Primary Metal Manufacturing
To this Code "3313" belongs the sub codes
NAICS Code 33131: Alumina and Aluminum Production and Processing