Composite insulators made from fiberglass rod cores with silicone rubber or EPDM sheds classify under 854690 (other materials), not under the ceramic or glass subheadings. The material of the insulating body — not the metal end fittings — determines the subheading.

Heading 8546 covers articles whose sole or principal function is electrical insulation — they support or separate conductors. The neighboring heading covers insulating fittings that are structural components of electrical machines or apparatus (such as terminal blocks or connector housings) and metal conduit lined with insulating material. If the article's primary role is mechanical assembly rather than pure insulation, it likely belongs in the fittings heading rather than here.