On a previous episode, we tested using plastic thread forming screws as fasteners for 3D printed parts. While they work great for some applications, they can only be removed and inserted a limited number of times before they destroy the hole and they are somewhat limited in their holding strength.
We have been hard at work the last few weeks developing some new products, and found this an interesting solution to the problem.
Since you also have to buy machine screws, they are a little expensive at $0.15 each, in quantities of 100. These brass inserts perform better than expected. The soldering iron tip makes them incredibly easy to install and the holding strength is more than sufficient for anything you would be 3D printing in plastic.
In a properly sized hole with a slight chamfer we were unable to pull out the inserts with our planned test methodology, and the tests were deemed successful.
ihrchive 
I remember seeing these on a few things I have taken apart, but never really considered using them myself. They actually look very useful, I'll be getting a few to test myself, thanks for the post.
Your link to the brass inserts doesn't seem to go to brass inserts…
Should be fixed now. It was supposed to go to http://www.mcmaster.com/#catalog/118/3291/=hi67gi
Can't you do the same with a standard nut?
You can probably insert a standard nut the same way, but I doubt it will have much holding strength. The grooves on the side are designed to keep the insert from being pulled out.
Can you list the specific part numbers you used (for both the inserts and the iron tips)?
93365A132 1 Pack Brass Threaded Heat-set Insert For Plastics, Tapered, 6-32 Internal Thread, .250″ Length
92160A119 1 Each Insert Tip For Soldering Iron, Installation Tip, #6 & M3 Internal Thread
Alternately try using helicoils
Spotted this on Make Blog. I work primarily with wood, but may have to try some of these inserts. I assume they could also be glued in.
Sometimes I need to screw something into wood that will be removed enough that the wood may eventually strip out. What I've been doing is to drill a hole large enough to insert an unexpanded plastic drywall anchor. Then instead of using the screw included with the anchor, I use a smaller diameter one; just big enough so that the threads grip well with minimal expansion of the anchor.
I've had great luck with this. Great holding power, no split wood, and if an anchor ever strips out it should be replaceable; though this has never happened.
While not as small and elegant as these threaded inserts, perhaps this may be of utility in fused filament parts too; with the advantage that you can get them at any hardware store.
Actually we have been looking at some inserts for wood as we would like to be able to thread some holes in laser cut MDF.
We tried Part #90016A007 Self-tapping Insert For Wood, Slotted Drive, 6-32 Internal Thread, 3/8″ Length
from Mcmaster and they split the MDF, but our starter hole might have been the wrong size.
Our “local hardware store” is either Fastenal or Grainger. However, since we get next day service with UPS ground from McMaster it's almost easier to just order the parts.
The convenience of Brooklyn for hardware startups.
Looking at McMaster-Carr, they have welded nuts of various sizes that would seem suitable. I have also seen 'hurricane nuts' or 'pallet nuts' in addition to metal 'speed nuts' are probably reasonable.