Subheading 903141 is reserved for optical instruments specifically designed to inspect semiconductor wafers, photomasks, or reticles. Optical measuring or checking instruments that serve other industrial purposes — such as coordinate-measuring machines with optical probes or optical comparators — fall under 903149. The end-use specificity to semiconductor process control is the key classification criterion.

Parts and accessories that are specifically designed for the measuring, checking, or profile-projection instruments of heading 9031 are classified under 903190. Heading 9033 is a catch-all for parts and accessories of Chapter 90 instruments that are not specified or included elsewhere in the chapter, so 903190 takes precedence for 9031-specific components.