2710.20.05.10 - Having a Saybolt Universal viscosity at 37.8˚C of 45 seconds or more but not more than 125 seconds (No. 4-type fuel oils)

This HTS category, 2710.20.05.10, specifically covers distillate and residual fuel oils that have been tested and found to have a Saybolt Universal viscosity at 37.8 degrees Celsius ranging from 45 seconds to 125 seconds. These oils are commonly referred to as "No. 4-type fuel oils" and are characterized by this specific viscosity range, which places them in a distinct operational category for heating and industrial applications. The inclusion criteria are strictly based on this measured physical property, differentiating them from lighter or heavier fuel oils.

The primary distinction between this category and its siblings lies in the specified viscosity. Category 2710.20.05.20 encompasses heavier fuel oils, defined by a Saybolt Universal viscosity exceeding 125 seconds. Conversely, category 2710.20.05.50 serves as a residual category for other fuel oils not meeting the precise viscosity specifications of the preceding subheadings within the "Testing under 25 degrees A.P.I." group. Therefore, the classification hinges on precise viscosity measurement at a standardized temperature.

As this is a leaf node in the HTS classification system, there are no further subcategories branching from 2710.20.05.10. This indicates that the classification is sufficiently granular at this level, with the described viscosity range being the definitive characteristic for goods falling under this code. Importers and exporters should therefore rely on accurate viscosity testing results when determining whether their No. 4-type fuel oils fall within this specific classification.