This tool first and foremost classified as a SAVE YOUR A$$ tool. Stripped out threads in sheet metal, blind holes, and other botched up threads are fixable with the Nutsert tool. This is not to be confused with the RIVNUT which is a similar product but is a bit different in how the insert holds into the material. And lets not forget the Timesert, which is one more insert. All are great at solving problems and fixing up threads in areas where you may not be able to re-tap or repair the threads. Also be careful about the lower end and pop-rivet like tools, they are not that good and securing the insert as the ones where you tighten it up. ALSO you can make your own tool in a bind, you just need the correct size allen bolt, an nut and the insert, it's a bit more difficult to keeps things straight and not spinning but it will get the job done.
Nutsert Tool Kit
This is an excellent kit. Again, not an inexpensive tool, but one that is well made. It comes with a sampling of Nutserts as well as all the mandrills for the various size of Nutsert.
This kit was purchased from Aircraft Spruce, also be available from McMaster Carr but they call them 'Rivet Nut Inserts'
Nutsert Mandrils Close View
These are the adapters for each different size of thread. The standard allen bolt is seen and can be easily replaced if stripped or broken. You could make your own tool with an allen bolt and a nut, but one thing is nice is the REAL tool grabs the nutsert with its serrated edge to keep it from spinning.
This is a picture (not mine) that shows the tool and how it would insert a Nutsert. Each size nutsert has a small allen bolt that is used to set the insert. Once you select the correct sized mandril you thread the insert on it and place in the 'CORRECTLY' sized hole (important) and hold the handle and twist until the insert is set. Be careful on smaller inserts you can easily over tighten and break the small allen head. Don't worry its just an allen head bolt and easily replaced. Ask How I know...
Close Up of the Nutsert
The inside of the Nutsert is threaded with your choice of thread based on what you need. The top lip is very thin and only protrudes a little over the top of the material. They are available in many different materials, most kits come with aluminum.
How the Nutsert Works
he fuzzy picture shows 3 images. The first is the Nutsert in the material un-swagged, the second is as it being pulled up and finally the completely swagged nutsert. The top lip is a very thin but does portrude over the top of the material. If you need it flush you can do a small spot surface to counter sink it, but in most cases you won't need to. They have many styles of Nutserts as well.
The NOT recommended kit
I had also picked up a different style kit with the idea it would be more like a pop-rivet and faster. These kits are like a modified cheep pop-rivet gun with a threadable mandrill. I have only had fair luck on the smallest Nutserts with these guns. They do not leave you with a good feeling of the insert being secure. Get the other kit or one where you tighten instead of pop!