The exclusion of metal-rolling equipment from 8420 is based on the machine's design and principal function, not incidental contact with metal. A machine principally designed to roll rubber or plastic that incidentally contacts metal fittings remains here. A machine designed to roll or reduce metal stock — even if it also handles other materials — would fall under the heading for metal-rolling mills. Principal use and machine design are the determining factors.

Yes. Cylinders for calendering and other rolling machines (excluding those for metals and glass) have their own subheading at 842091, separate from other parts at 842099. When imported separately, cylinders should be classified under 842091 rather than as general parts, provided they are identifiable as designed for these machines.