How well do rivet nuts hold? I talked to a couple of metal guys and they said that rivet nuts should only be used on light load stuff.
Well, it depends... [MENTION=66316]1engineer[/MENTION] can probably throw some of his experience, I believe he deals with aircraft; where they tend to use RivNuts a lot from my understanding. [MENTION=70181]Gatafly[/MENTION] also mentioned he uses them at work, I am not sure what for though.
A LOT of sections of modern vehicles use rivnuts, typically lower load areas, or blind sheetmetal/metal sections. But if you match the thickness of your base metal with the correct range of rivnut (they have different grip ranges to better accommodate the material, I used ones ranged for 0.027 to 0.150" to repair damaged factory nuts in the frame for the skidplates) and torque/install them properly you should have no issues.
I am running a full set of RCI 3/16" skidplates on my 4Runner, part of the bolts go into Rivnuts I used to repair stripped out nuts in the frame. So far they haven't ripped out of the frame despite serious impacts off-road, enough to dent 3/16" plate steel.
I can sort of answer your question but first let me give you a bit of background material so we are all on the same page:
Newton - A Newton is a unit of force that is equivalent to 1 kilogram per meter divided by seconds squared. Why do you need to know this? Because the Rivnut chart is in Newtons and you need to understand that force units are different than just plain pounds or kilograms.
1 Newton is equivalent to 0.22481 lbF so it takes a bit over 4 lbF to equal 1 Newton.
Rivnut Data - Here is the basic data on Rivnuts
http://www.technologycomponents.com/pdf/RIVNUT Catalog_Complete.pdf and pages 13 and 38 for example is where they talk about axial loading.
This can of worms can get complicated real fast so I am going to be very general in my explanation.
Comparing a stainless M8 Rivnut to a typical M8 Nut and bolt, the Nut and bolt is stronger. That is not to say the Rivnut is weak. No, it is plenty strong DEPENDING ON THE APPLICATION. For example, the max axial loads on an M8 Rivnut is about 6K lbF. That is pretty good! Good enough for a lot of jobs. The challenge with applying Rivnuts is threefold:
1. Choosing the right Rivnut for the Application
2. Using the proper tooling to apply the Rivnut
3. Choosing the right material.
So if you have all the proper tooling to install the Rivnut correctly and you have chosen the correct Rivnut and material then you should be fine. If you guessed at any of these then your fastening job will be just as good as your guess lol. Regular nuts and bolts are fairly easy to apply and fairly simple to understand. Let me put it this way: If my life depended on me hanging from a steel cable supported by either a Rivnut or a conventional nut and bolt and they had "Bubba" over there doing the figuring and install, I would choose the nut and bolt.
