A turning center with live tooling that can perform milling and drilling in addition to turning may still be classified under 8458 if its principal function is turning. However, if it meets the definition of a machining center — including automatic tool change from a magazine — it could fall under the machining-centers heading. CBP binding rulings have addressed this boundary, and importers of combination turn-mill machines should seek a ruling for certainty.

Importers generally support the NC classification with technical specifications, the machine's control system documentation (e.g., CNC controller model and program-input capability), and the manufacturer's product literature. CBP may request these at entry; having them prepared in advance reduces the risk of a reclassification to the non-NC subheading.