Expansion locknut for Ford car models

The locknuts, holding the screws for the underbody guard of our Ford Focus MKII failed due to aging plastic and ice buildup. Ordering replacements would have taken over a week. Also, I really didn't feel like paying the equivalent of a filament spool plus shipping for a few grams worth of plastic, so…

… I designed and printed my own replacement part! :-)

Before installation

• This should be obvious, but as this is no original part, use it at your own risk! I installed it on my personal car and it has held up well so far - so I wanted to share this with the world. Yet I will accept no responsibility in case this part fails, anything gets damaged or anyone gets hurt!
• With this out of the way, there are a few things you should check for:
  • Strong layer adhesion: There should be a strong bond between the baseplate and the two “arms” of the locknut, as this is where all the mechanical stress will be induced.
  • Tight fit: The locknut should snap tightly into the square 10 mm chassis holes. This makes sure that it will actually grip, once you insert the screw. If it is too loose, adjust for your printers tolerances.
  • Don't overtighten: The original locknuts actually tend spin in their slot. The screws only secure the underbody guards tight enough to keep it in place. A (little!) bit of movement is OK for vibration dampening. If you overtighten the screw, you might end up turning it inside the thread, which is not good. If this happens, remove the nut and print another one.
• Tip: I designed the hole for the screw to be a very tight fit, to make sure the screw really cuts intro the material. I would recommend to screw it in half way once before inserting the locknut into the chassis (see picture). This will make installation a lot easier.

Recommended material and print settings

• TPU/TPE or similar - I would not recommend anything stiff or brittle like PLA as this part will be exposed to a lot of vibrations. The material I used was a shore 98 TPU. 
• Max volumentric speed: 4 mm³/s - This is a typical value for flexible filaments that works well for me. You should of course adjust for your specific filament type and printer.
• No supports, no brim
• 100% Infill

I would love some feedback if you printed this model - so please upload a picture of your makes!

Happy printing!