The US manufacturing sector is too large to fit within a single two-digit NAICS code, so it is split across codes 31, 32, and 33. The division is administrative rather than reflecting a sharp industrial boundary; analysts typically aggregate all three when measuring total manufacturing output or import competition.

NAICS codes describe domestic production establishments, while HTS codes classify imported goods. Concordance tables published by the Census Bureau and USITC allow analysts to bridge the two systems, but the mapping is approximate — a single NAICS industry may correspond to multiple HTS chapters, and vice versa. Direct HTS-level analysis is always more precise for tariff and trade-remedy purposes.