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I've been scouring the internet for hours to find this type of nut. The requirements are fairly simple:

  • I want to cut holes into two metal sheets to join them with some kind of fastener (e.g. nut and screw).
  • The fastener should be removable.
  • The thread should not touch the sheets, so I would like to embed the nut into the hole.
  • The nut and hole should not be circular to prevent the nut from rotating.
  • The nut should have some sort of head protruding beyond the hex shape, to keep the metal sheets from separating.
  • Bonus: The nut should be open, so it doesn't limit the length of the screw.
  • Bonus: The sheets are about 2mm each. It would be perfect if the embedded part of the nut was 4mm long.

At first, I thought this would be simple. Just order a flange hex nut and a screw. To my surprise all flange hex nuts I could find are supposed to be installed the other way around and the hex part can't just be embedded in a hex shaped hole to protect the thread, because the flange is not flat on the side pointing towards the hex nut.Then I started looking at sleeve nuts. But I can't find any with a feature that prevents the nut from rotating. Every single one I found is round.

I would be very happy for any answers or hints for the following questions:

  • Where can I order this?
  • Why is this apparently not a commonly used fastener (am I missing an obvious alternative solution)?
  • What is this called?

Below I added a drawing of a possible solution. I'm not married to the hex shape, as long as the shape has some feature that prevents the nut from rotating in the hole: top view bottom view

cg_f
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2 Answers2

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Blind hex-shank rivnut. You can get partial and full hex shanks, different heads, etc.

https://www.bossard.com/eshop/global-en/search/?q=fasteks+filko&productId=BN-25501-M630-HEXTSN-A2-M6-%2F-0%2C53

FASTEKS FILKO® HEXTSN

https://www.boltdepot.com/Product-Details.aspx?product=27726&qty=100&gclid=Cj0KCQiA45qdBhD-ARIsAOHbVdH7gHXglb5eU5tQm3tXtQ6GNW9l5mf4c0h1sHzHqSfug9wSwbQfb9EaAu4bEALw_wcB

SAE sizes in zinc plated steel

Phil Sweet
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  • I stumbled over those in my search. If I understand correctly they all have a thin threadless grip range, which is supposed to deform to grab the sheet during installation. That makes them permanent and the resulting protruding flange on both sides of the sheet they are installed in would prevent the second sheet to be joined without a gap. This, but without grip would be perfect though. – cg_f Dec 25 '22 at 12:13
  • Okay. I couldn't find exactly what you are looking for either, but the normal solution is called a "trailer nut" It has a domed flange, and as long as the washer on the bolt-side is not bigger than the flange, the trailer nut will grab and not spin. But you need access to both side to get it started, or a tight fit initially. https://shop.stafast.com/pallet-nuts/trailer-nuts – Phil Sweet Dec 25 '22 at 15:59
  • Also, flush rivnuts exist. https://www.grainger.com/product/GRAINGER-APPROVED-Rivet-Nut-Aluminum-5NNK7 – Phil Sweet Dec 25 '22 at 16:04
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It's difficult to be certain of your specific objective, as the sheet of metal is missing from the diagram/photos, but I suspect that a nut spot welder may provide what you seek.

A number of videos are online, including one in an industrial setting; a rather large fixed machine performing the welds. Another video appears to use a less-industrial, but still commercial-grade spot welder with a custom socket to hold the nuts.

One could envision modifying or adapting a portable spot welder to accomplish this task. I recently required to secure a nut to a steel tube in a similar manner. The hole was drilled, a bolt and nut placed in position and three spot welds were applied to alternating flats. No electrical spot welder was involved, rather a MIG welder provided the bonding.

One could use brass nuts and possibly braze or solder them in place. More details in the post are warranted to exclude this type of options as needed.

Rivnuts are an option that you have explicitly excluded, as they are cylindrical and if not properly secured to the sheet, will rotate under sufficient applied torque.

fred_dot_u
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