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I think you actually have a categories of categories problem. You have an ink system and should list all the members of it -- the gauge is one member. So there's a category of categories... systems. You also have part types... gauges are one part type, and you should list all gauges -- with links to the systems they support. It would be helpful to give the reader some clues about how she's reading... Am I looking at members of a system, or just all parts of a certain type?
The vacuum pump gives the same problem... You have one or more vacuum systems, and you have types of parts that get thrown into vacuum systems.
So I say, list both. But make it clear that the two lists are different categories of category.
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