Background to the question: We have been importing lug bolts under a certain tariff heading which is under dispute :

The crux of the question is whether the lug bolt ( which we have ascertained is in fact a screw ) is deemed to be fully threaded or not. The definition of this would determine the tariff heading that would be applied. Namely a separate tariff heading for a screw that is fully threaded and a different one for a screw that is partially threaded. The question here is because of the design of this screw, namely with a seat is it considered to be fully threaded or not?

I have attached below a picture / link of the type of lug bolt I am talking about.

enter image description here

  • $\begingroup$ Comment only. You probably need to say what YOU think to add perspective. My opinion carries no weight at all but I imagine from what you say that you are arguing that the bolts/screws are fully threaded as the seat necessarily is unthreaded so if the seat is included in the consideration it is impossible to ever have brews (or scrolts) of this sort fully threaded. So IF there are categories for fully threaded and not fully threaded bewlts in this type of fastener these ones MUST be fully threaded. However this is mere semantic pedantry and the sort of people who administer this area .... $\endgroup$ Commented Jul 28, 2015 at 14:00
  • $\begingroup$ ... will speak and write MSP by the hour but not be moved by it so odds are you are out of luck if the above is your argument. Also equally out of luck if you want to argue the other way when arguing with MSP purveyors. | But: Fully threaded. | IF they argue they are not FT AND if you want to say they are FT then the easy question is "what would a FT versin look like if this is not one?" | If you are wanting to argue the opposite do not show them this argument :-) $\endgroup$ Commented Jul 28, 2015 at 14:03
  • $\begingroup$ FWIW: The whole subject is MSP and utterly ludicrous in this context as no tariff difference SENSIBLY applies to this distinction. Alas, sensibility logic and truth are not relevant in such things. $\endgroup$ Commented Jul 28, 2015 at 14:04
  • $\begingroup$ This is a question about legal definitions, not an engineering question. That being said, if you want an answer it would be helpful to be able to read the full text of the tariff law under which you are being taxed. Can you add enough information to look it up (country, municipality, statute number, etc.)? $\endgroup$ Commented Jul 28, 2015 at 15:42
  • $\begingroup$ It is up to the policy-makers to provide a strict, comprehensible definitions of any and all products to which a tariff applies. Of course, that can be very difficult, especially when the policy-makers (who are unlikely to be subject matter experts themselves) have limited support staff. Most likely the dispute has arisen because the tariff law was not written with this special case in mind. I see this question as asking for an engineering perspective on the matter, which could be useful for building an argument for how the law should be interpreted, as well as generally instructive. $\endgroup$
    – Air
    Commented Jul 28, 2015 at 15:55

1 Answer 1


From a purely functional perspective, I'd argue that the seat is irrelevant to whether a fastener is fully threaded. The seat is functionally part of the head, not part of the shank, and the shank is all that's relevant here.

First, consider that the largest diameter of the seat significantly exceeds the O.D. of the fastener. This indicates that the seat is forged from the wire rod (as is the head) rather than cut or rolled (as are the threads).

Second, the function of the seat is to mate with an external surface (like the head) rather than with internal threads. This is true even if that external surface is not perfectly flat, or if the hole is counter-bored; the force on the head or seat acts to push the fastener out of the hole, while the force on the threads acts to pull the fastener into the hole (when used as a screw).

There may also be unthreaded chamfers at either end of the shank of a "fully-threaded" bolt, for ease of starting nuts and/or to make sure failure doesn't occur right at the joint of the head and shank. The presence of these small chamfers doesn't prevent a fastener from being "fully-threaded." So I think the engineering perspective is clearly that the "lug bolts" (which you correctly point out are used as screws, despite the name) you've shown above are fully-threaded fasteners.


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