This is a 3D printed case for the 4-Player Adapter from Individual Computers.
The 4-Player adapter (sold by Individual Computers, https://icomp.de/shop-icomp/en/produkt-details/product/id-4-player-adapter.html#filter=* ) plugs to the user port of the C64, C128, VIC-20 or CBM610 computers. It was originally used by the Commodore 64 game "Bombmania", but has now turned into the de-facto standard of 4-player solutions for the Commodore 8-bit line. It is supported by the following games:
Alone in the Green
Snacks 4 Snakes
Ivan 'Ironman' Stewart's Super Off Road
Tour de France 2005
Although mechanically compatible, this adapter does not work on the Commodore plus/4.
Two M2 heatsets and M2/6mm cap screws are required for the assembly of this case. They can be obtained here: