If you have never used Riv-Nuts - you have missed out! They are the most marvelous invention for inserting a captive nut into a panel where you do not have access to the back of the panel.
They work in a very similar way to 'Pop Rivets' and are quick & easy to use. They require a special tool that can run about $40. So what happens if you do not have access to a RivNut tool and either need to install a RivNut OR have to tighten one down (for some reason). Make your own! Granted, if I were going to install 100 RivNuts, I would by the RivNut tool but if you only want to install a few of them, you can use this tool instead and save the $40. The tool consists of a bolt (actually a machine screw if you want to be technical) a washer and a nut with the thread drilled out.
Drill an 11.5mm hole in your panel.
Here you can see the tool on the left and the Riv-Nut on the right.
Slide the nut (with the thread drilled out) over the bolt and screw the Riv-Nut on to the end of the bolt.
Insert the whole thing into the hole you drilled in step 1.
Using an open-ended 13mm spanner, hold the nut still.
With a ring spanner (or socket + wrench) turn the bolt clockwise. The Riv-Nut should not rotate. There should be enough friction between it and the nut to hold it still. If not, a blob of Super Glue (tm) between the nut and the Riv-Nut will help.
As you tighten the bolt, it pulls in the back of the Riv-Nut collapsing the tube against the rear of the panel.
As you tighten it, you will feel the bolt become more difficult to turn. This is the time to stop! The Riv-Nut will feel securely fixed in the hole.
The Picture on the Right shows the back of the Riv-Nut when secure.
Remove the bolt from the Riv-Nut.
And that's it!
If, even after applying Super Glue (tm) between the nut and Riv-Nut, the Riv-Nut still rotates in the hole, try applying a blob of glue between the Riv-Nut and the panel.