Because they fall into an automotive classification, they fall into the section 232 steel & aluminum derivatives tariffs. You have to pay a tariff on the value of the steel or aluminum parts that are in there, unless you can prove they were smelted in the USA. The 232 rules predate all of the current trade war tariff issues. Technically you are supposed to declare the country of smelt on these parts as well, and if you don’t know, you are supposed to declare Russia, or some other highly sanctioned country.
As the importer of record, you are legally the person that is supposed to know these answers, so telling CBP, I don’t know, ask TROA is a higher risk scenario. Ever since the customs modernization act of ‘93, it is the importer’s responsibility to know what they are doing, blah blah blah.
Although more often than not, a fedex rep would just click the box that says “no metal” & move on without asking. They’ll get more hardcore about it with all the changes this year.