Hey CD…
We have a 1"x1" tube with 3mm tube thickness that the bumpers will screw into. The holes that the bumpers will screw into will be tapped with M6. We want to improve our bumpers this year and unsure if this is the best option. 
Have any of you used Rivet Nuts/Nutserts for bumper attachments? And how well has it worked? Is it better than just tapping tubes or not much of a difference?? 
https://www.bunnings.com.au/kincrome-m6-rivet-nut-insert-20-pack_p0316236
The nice thing about rivnuts is that you get more thread engagement than simply tapping into the tubing, as well as stronger threads than you would get in aluminum. The danger is that you overtorque your bolt and spin your rivnut which is then a pain to get out. I’ve found that as long as you use a good installation tool the spinning is rare, but it’s something to be aware of (we had a season once where we could only find our bad rivnut tool and that didn’t go well).
I prefer to use a threaded standoff for mounting bumpers - though you need a hole on the opposite side of the tube to bolt it in place.
I hate Rivet Nuts for bumpers. Have had horrible luck with rushed students crossthreading bolts, which then leads to breaking out the angle grinder. Also have had bad luck with the rivet nuts loosening, but not enough to extract, so loosening tightened bolts becomes impossible.
We used rivet nuts on our 2022 robot, they sucked. They would cross thread and are a pain to replace every couple of days. I would recommend trying to use a square nut instead in a 3d print to get a similar effect.
I do not recommend tapping a 3mm thick tube wall for an M6 bolt, even if that tube is steel it is not enough thread engagement and your bolt will strip out the threads, especially over repeated installs.
You can make a little “nut plate” that you rivet onto the underside of the tube, and then your bolt can go all the way through the tube and thread into this plate.
Sharing what we did with imperial dimensions:
Or buy. McMaster-Carr (You might find them cheaper at an aerospace supply shop, or similar–as well as drill tools to allow you to set the inserts easier.)
There’s a few other options for similar types if you look up “nut plate”. Some of them are clip-on, some weld on.
We’re considering using a rivnut, then locktiting a threaded stud into the rivnut and mounting the bumper to that stud using just a wing-nut. Seems like a lot less risk of cross-threading and over-tightening.
Any opinions on that?
We’ve only had a couple instances of problem with rivnuts over the years. We use them all over the place on our robot including our bumpers. With that said we use them to bolt down a quick release clip for bumper attachment and are not running the bolts in and out all the time. I would not suggest them being used like you mentioned but rather for fastening down a quick release system
We have used riv-nuts in the past, My preference is if you go the threaded in route they are your repair once you strip the thread, but they are durable enough to do the job.
I personally think installing bumpers onto a stud is easier, faster, and more reliable so I’m not really a fan of this overall concept.
Thanks for the reply! 
Putting a nut into a printed part was also one of our considerations!
If you have hex broaches you can really easily make your own captured nuts. 3/8” hex = 10 nut 1/2” hex = 5/16” nut. We broach a small aluminum plate and add a small 3D print or thin poly cover to retain a locknut, then when the nut wears out you can change the nut. It’s a slightly more involved fabrication process, but it lasts a long time, is repairable, and is locking.
I have done rivnuts in the past. They worked, but the other posts in this thread describe some of the issues (cross threading, spinning the rivnut, etc.) and they are a pain in the butt when those things happen.
I have also used dzus 1500 slide latches (or knockoffs of them) which worked pretty well.
Currently we have our eyes on the plummer industries kit (there is a voucher for a slight discount in the KoP) but they are a bit spendy. Cry once, buy once? They look amazing.
Yes, we use them for bumpers currently in 5934.
A few helpful tips:
Get a short piece of threaded rod or a stud and put that into the rivet nut, secured with thread locker (blue). Now use wing nuts (or similar) to secure the bumper - all but completely eliminates the cross threading under pressure issues (just replace the stud/wing nut if you need to)
Make sure bumpers are constructed such that the nuts just hold the bumper in place, side impacts are transferred to the frame instead of through the nut. This keeps them from getting loose.
You can install them with retaining compound (green loctite) as well, before they get set into the tube.
A different but similar option that we have had good luck with is Clip Nuts:
We have typically used coarse thread 1/4-20 clip nuts for attaching bumpers several times. If installing in box tube, you will have to make an insertion hole or notch for the. They work really well on sheet metal, plate, or U channel, but automotive uses them all the time in box beams.
Pros: Steel threads, don’t need a wrench, easy to install on plates/channels, easy to replace. Easy to find replacements at hardware store, autozone, or online.
Cons: If installing in box, requires two holes. One for the fastener, and one hole/notch for installing the clip.
I love rivnuts, but always worried about this failure mode, it is a pain.
This thread inspired me to this solution: Make your own “nut plate” with a rivnut in the middle, and two regular rivets either side to connect to the frame. If the rivnut fails, drill out the rivets. (Center hole in frame may need to be drilled out a little larger so rivnut slips inside)
Or you can buy them. They aren’t that expensive:
I would still be a little concerned about the rivnut spinning out. If the nut is tightened correctly every time, then it should be fine, but if it’s loose it could put extra load on the stud, elongate the hole, and cause the rivnut to spin out sometime after that when switching out your bumpers.
We have used rivet nuts in the past for mounting bumpers- not recommended. They will tear out of the aluminum when the bumpers are hit during defense. They work , but not for long.
Ah, but if you want a 1" mounting hole distance the cheapest is $3.85. But I take your point. Rivnuts aren’t free either.
Hands-down my favorite bumper mounting system: a threaded rod/bolt end sticking up, then a wingnut holding the bumper bracket down to it. Swapping sets is so fast when you don’t have to swap the bolts every time, too.
Systems like this are also so easy to put together & use that, as an RI, when I need to build a team’s bumpers with them at an event (happens more often than you think) that’s what I go for.