8402.90.00.90 - Other

This HTS classification, 8402.90.00.90, encompasses "Other" parts for steam or other vapor generating boilers, excluding those specifically listed under other subheadings. This residual category is intended for components that are essential to the functioning of boilers covered by heading 8402 but do not fit into more specific classifications, such as heat exchangers.

It is crucial to distinguish this category from its sibling, 8402.90.00.10, which is exclusively for heat exchangers. If a boiler part's primary function is to facilitate the transfer of heat between fluids or gases, it should be classified under 8402.90.00.10. This "Other" category, however, covers a broad range of components such as pressure gauges, safety valves not specifically designed for heat exchange, insulation materials, internal baffles, supports, or any other non-heat-exchanging part integral to the operation of the boiler.

Given that this is a leaf node, there are no further subcategories. Therefore, classification into this subheading relies on the part being identifiable as belonging to a boiler under heading 8402 and not being explicitly covered by any other subheading within 8402.90. The classification hinges on the absence of specific descriptive subheadings for the component in question.