Unmounted friction materials — brake pads and linings not yet assembled into a brake assembly — classify under 6813. Once a friction element is incorporated into a complete brake assembly or sub-assembly designed for a specific vehicle, classification may shift to the relevant vehicle parts heading. The mounted versus unmounted distinction is the primary classification test.

While 681320 remains an active tariff line, commercial trade in asbestos-containing friction materials is heavily restricted by EPA TSCA regulations and has declined sharply. Most brake pads and linings entering US commerce are asbestos-free and classify under 681381 or 681389. Importers of any asbestos-containing friction material must comply with TSCA certification requirements.