How to Install and Use Rivnuts FAQ
I guess that these are called Rivnuts / Riv-nuts / Riv nuts / Blind Nuts / Nut-sert
or in generic terms, a blind-hole rivet containing an internally threaded hole for use on thin materials.
On your bike, the water bottle holder attaches to riv-nuts. Look closely and you'll see the threads inside the hole where the bolts go in.
Anyway, I needed to use them to mount my battery box to my thin aluminum frame. I considered putting bolts straight through, but I was pretty sure it would crush the tubing. It's a good thing I didn't try that, after seeing how thin the metal was, I'm definitely sure that it would have crushed.
Rivnuts come in aluminum and steel. I could only get the aluminum kind at my local specialty fastener store.
The process of setting a Rivnut is very simple, but because this sort of thing isn't something we do every day, it is very confusing to explain in words, but I'll try.
1. drill hole to fit rivnut (ideally the hole should be small enough that you have to tap very lightly to get it to go in)
2. put rivnut on tightening device
3. tighten rivnut device
As you can see just the words are about as useful as having the perfect size wrench for a completely stripped nut. Before I show you my pix, here are some tools you can use:
Pro Rivnut setting Tool
Homemade rivnut setting Tool
Cute cheap commercial setting tool
My version is made from what I had around, but it works pretty well. The Allen head bolt holds the rivnut still, and the nut moving down the bolt pulls the rivnut into compression. The two washers are necessary, as well as a bit of oil between them. If you only use one washer, the nut rotation turns the washer, and the washer rotates the rivnut in the hole.
This is bad because if the rivnut rotates, it may accidentally enlarge the hole you drilled. Large hole means the rivnut falls out and never becomes secure. This may be less of a problem on steel, but it sure is a problem on thin aluminum like on my bike frame. I had to do two over before I realized why it was happening. The oil helped a lot too.