9031.90 - Parts and accessories:

This HTS category, 9031.90, encompasses a broad range of parts and accessories specifically designed for use with instruments and apparatus classified under heading 9031. This heading covers measuring or checking instruments, appliances, and machines not elsewhere specified in Chapter 90, including profile projectors and test benches. Therefore, the items classified here are components or supplementary items that facilitate the operation, repair, or enhancement of these sophisticated measuring and testing devices. Examples include lenses, mirrors, stands, power supplies, and specialized tooling for machines that balance mechanical parts, test benches, profile projectors, and other optical instruments.

It is crucial to distinguish this category from its sibling headings which cover complete machines and appliances. For instance, 9031.10 covers complete "Machines for balancing mechanical parts," whereas 9031.90 would cover replacement parts for such machines. Similarly, 9031.20 covers entire "Test benches," while 9031.90 would cover components like specific sensors or fixtures used with test benches. The category "Other optical instruments and appliances" under 9031.80 pertains to the finished optical instruments themselves, not their constituent parts.

The subcategories within 9031.90 further refine the classification based on the specific type of instrument the part or accessory is intended for. "Parts and accessories of profile projectors" (9031.90.21) are for projection-based measurement devices. "Parts and accessories of other optical instruments and appliances, other than test benches" (a further subdivision not fully detailed here but implying optical measuring devices like comparators or optical scanners) distinguish components for a variety of optical measuring equipment. Finally, "Other" serves as a residual category for parts and accessories not falling into the more specific subdivisions, ensuring comprehensive coverage for all components related to heading 9031.