The decisive criterion is self-propulsion. Machinery that moves under its own power — bulldozers, excavators, graders — belongs in 8429. Equipment that must be towed, pushed, or mounted on another vehicle, such as towed scrapers or non-self-propelled boring rigs, falls under 8430. For combination units, the principal-function and self-propulsion tests both apply.

Compact or mini-excavators with a 360-degree revolving superstructure are classified under 842952 regardless of their size, provided they are self-propelled. Those without a full 360-degree revolving superstructure may fall under 842959 as other self-propelled mechanical shovels and excavators. Weight or engine size thresholds do not determine the subheading; the structural configuration does.