They show up as either "vias" or "hollow grommets":
< https://www.ebay.com/sch/Other-Fasteners-Hardware/42905/i.html?_from=R40&_nkw=vias >
Roy
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Re: Slightly OT: What are these called?
2017-10-16 by roylowenthal@...
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2017-10-16 by roylowenthal@...