Note: the original file will need to have the bolt pressed in with a vise. The wider one should work as described below.
This is the knob that holds down the spare tire in a new beetle. I'm not sure about the years this will work on, but mine's an '04, so probably at least '98 to '04? The knob has a tapered wall before the hole for the bolt's head to retain the bolt.
I made this a remix of pavel's knob because they were here first. Had I known their model was online, I probably would have just printed theirs. I like mine better simply because I think it matches the original better and because it's my own. However if this model doesn't work, check out theirs and see if it fits.
Because of heat in the vehicle, and the fact that it's attached to the frame of the vehicle, you should probably print this in something other than PLA.
If you print with the largest face on the bed and you'll need a little bit of supports in the hole. If you print with the smallest face on the bed and you'll need supports under the whole knob, but you won't need to clean the hole for the bolt's head as carefully.
Remove the supports, making sure to clean out the wider area under the taper for the head of the bolt. This is where the bolt will actually sit.
Push In Bolt
Seat the bolt in as far as it will go. Don't worry if it doesn't go in all the way.
Seat the Bolt Completely
For the original: Press the bolt in with a spacer and a vice, hammer, or other tool.
For the "wider" file: Screw the bolt partway into the hole for your spare tire and pull up to seat the head below the taper. Alternatively, tighten the bolt until it's pulled into position by the the pressure against the wheel.
You're now set. Put the tools back into the wheel as usual and fold the carpet back.