I suspect there's probably high stakes involved for somebody, at some point in the fastener supply chain, based on whether their product is classified as a "scr

I suspect there's probably high stakes involved for somebody, at some point in the fastener supply chain, based on whether their product is classified as a "screw" or a "bolt". E.g. there could be different import duties on screws vs. bolts based on the location of manufacture. (I'd hazard a guess that duties on screws are lower, while bolts are higher, because protecting the domestic structural bolt industry was probably viewed as more of a national interest at some point.) There's also some grey area between "screw" and "bolt" particularly when you get into what are conventionally called 'machine screws'. For instance, you can get very large socket cap 'machine screws' that are the size, and could easily serve the purpose of, large hex bolts. The only difference is the use of an internal hex head vs. an external hex, which doesn't matter all that much given modern drivers. It would seem, based on the CBP's definition, that a socket head "screw" of any size would be a screw as long as it's continually threaded, but the moment it has any amount of unthreaded shank, it might be classed as a bolt. So it's not surprising to me that the document exists, although the fact that it does exist hints at the byzantine nature of the Customs system.