This part is designed to allow you to mount a 1-DIN car stereo into a 2-Din slot. DIN is generally defined as 180X50mm, so a 2-DIN is 180X100mm. Many cars come with a 2-DIN sized manufacturer radio, while many aftermarket radios are 1-Din, necessitating a part to fill the gap in the front panel. In my case the car in question is a 1996 ford explorer with a 2-DIN radio slot. After the stock radio broke a few years ago I got a new radio that came with a mounting kit. After that radio got stolen the insurance sent us a radio that came with a mediocre mounting kit that promptly broke, so I designed and printed my own. The adapter mounts a Pioneer P5100UB head unit into the slot of a 1996 Ford Explorer, however DIN sizes tend to be standardized, making it possible that this unit will work for other vehicles, which is why I decided to post it.

Features:
The adapter has a large opening in the front to allow you to store CDs, remotes, papers, etc. There is a little lip on the front to prevent stuff from sliding out when you accelerate. The coolest feature is the three 5mm holes and channel on each side. These are intended for you to insert 3 LEDs and run the wiring through the channel so as to create a neat lighting effect. I found the coolest effect to be from producing the plastic parts entirely in Nuclear Green ABS: http://store.makerbot.com/nuclear-green-abs-1kg-spool-3mm-filament.html
The LEDs were UV: http://www.radioshack.com/product/index.jsp?productId=3107633
This creates an effect where the lighting comes almost entirely from the fluorescence of the plastic and is thus much more diffuse and less likely to glare into your eye while driving at night. It's also just very unique looking.

Note: In the third image from bottom the apparent double image of the 3 LEDs is caused by reflection off the top plastic surface, showing how shiny it is after treatment with acetone.
The bottom image is how the radio/lighting setup would appear from the vantage point of the driver looking down at night.
The top image of course looks straight in and is far brighter than the driver would see. Still it is important for safety reasons to wire it to an external switch rather than just wiring it to the ignition or the instrument light control so that it can be switched off manually if it becomes too bright or distracting.