CBP generally applies the 'incomplete or unfinished article' rule under GRI 2(a): if the sections together constitute a complete TBM and are imported together or under a single contract, they are classified as the complete machine. Importers should document the assembly relationship of each section and consider requesting a binding ruling to avoid reclassification at entry.

The operative distinction is whether the cutting or boring unit advances under its own power. A roadheader or continuous miner that moves on crawler tracks driven by its own hydraulic or electric system is self-propelled (72335). A cutter head or drum that requires a separate carrier or haulage unit for movement falls under the non-self-propelled heading (72343). Manufacturer technical sheets specifying the drive and propulsion system are the key classification evidence.