After years of having a 3D printer I finally put it to use to fix something like I said I would. Long story short, the tweeters in the car burnt out and I ordered replacements but the mounting plate the replacements came with required me to drill a hole into the plate to fit the speakers, and though this would have been an excuse to buy a holesaw, I opted to just spend at least 4 times the amount of time to model the correct part in FreeCAD and print the part.
After some measuring and two quick iterations with very thin drafts to make sure everything lines up I managed to get the dimensions correct.

Render of the model
In the car it fits like a glove.

Draft Print fitting nicely onto the mounting points
Now I’m waiting for the full strength print to finish and install the plates and speakers. Very pleased with how I managed to pull of the 3D model with only minimal amounts of swearing.