The principal-use test applies: the article must be dedicated to use in electron tubes or CRTs and not suitable for general electronic applications. Components like shadow masks, electron guns, and getter rings are typically accepted as tube parts because they have no practical use outside a tube envelope. General-purpose items such as standard resistors or capacitors used in tube circuits would not qualify and must be classified under their own headings.

Yes, though volumes are much smaller than at the technology's peak. Ongoing demand comes from refurbishment of legacy industrial monitors, medical imaging equipment, and arcade/gaming restoration markets. Some specialized CRT manufacturers in Asia continue to produce tubes for niche applications, sustaining a residual parts trade that importers in the repair and restoration sector still need to classify correctly.