Classification follows the principal function. If the article is primarily a ballpoint pen with an incidental stylus tip, it falls under 960810. If the stylus function is primary and the ballpoint secondary, classification may shift outside this heading entirely. A binding ruling from CBP is advisable for combination articles where the principal function is not obvious.

Yes. Ballpoint pen refills — the ink cartridge and tip assembly sold as a replacement unit — are specifically provided for under 960860, separate from complete ballpoint pens at 960810. Importers should ensure invoices distinguish complete pens from refill units to avoid misclassification.