Crankshafts and camshafts are specifically named in the HTS schedule and typically occupy dedicated subheadings within the broader transmission-shaft heading. Other rotating shafts — propeller shafts, line shafts, stub shafts — fall into residual subheadings. The key classification evidence is the part's design function and the machinery it is intended to serve.

Engine remanufacturers generally require dimensional inspection reports, material certifications (confirming alloy grade and heat treatment), and surface hardness test results. For OEM-equivalent parts, some buyers also require compliance with original equipment specifications or third-party dimensional audits before accepting imported crankshafts into their production line.