When a part is physically interchangeable between spark-ignition and compression-ignition engines, classification turns on the engine type for which it is primarily designed and marketed. Evidence includes the manufacturer's catalog description, the part number's application list, and sales data showing the predominant end use. If the part is genuinely dual-use with no clear primary application, classification may require a binding ruling from CBP.

Remanufactured engine parts are classified the same as new parts under SITC 71391, but they may be subject to country-of-origin marking requirements that differ from new goods if cores were sourced internationally. Some states also impose environmental or warranty disclosure requirements on remanufactured components. Importers should also verify whether any applicable antidumping orders cover remanufactured versions of the specific part.