9027.90 - Microtomes; parts and accessories:

This HTS category, 9027.90, specifically encompasses parts and accessories for the instruments detailed in heading 9027. While heading 9027 as a whole covers a broad range of analytical, measuring, and checking instruments utilizing various physical principles, 9027.90 is dedicated to the components that comprise these sophisticated devices. This includes items such as specialized lenses, detectors, sample holders, pumps, and other essential components that facilitate the operation of instruments like spectrometers, chromatographs, and viscometers.

It is crucial to distinguish 9027.90 from its sibling categories, which classify complete instruments rather than their constituent parts. For instance, while 9027.10 covers gas or smoke analysis apparatus, and 9027.30 covers spectrometers, this subheading only applies if the item in question is a component *of* such an instrument, not the instrument itself. The classification hinges on whether the item is a standalone, functional instrument or a part designed to be incorporated into one.

Within 9027.90, a further distinction is made between complete microtomes (which are a type of precision instrument used for cutting thin slices of material for microscopic examination) and the broader category of parts and accessories for all other instruments under 9027. Therefore, if an item is a component of a microtome, it falls under the "Microtomes" subdivision, whereas parts for any other analytical or measuring instrument covered by 9027 would fall under the "Parts and accessories" subdivision.