A slim case for a module you built to Commodore 64's user port connector. In my case, I put to the case (besides the connector) a ESP8266 MCU+WiFi module. With the firmware I made it can be used to create telnet connections over Internet with old serial terminal programs to some BBSes and MUDs that still are used.
The case has a hole that can be used for a cable, LED, switch. Colorless plastic is nice to see through LEDs on PCBs. The lid part is actually a bottom cover which snaps in place because it is slightly tight. A standard user port connector can be screwed through the screw holes from inside the case to the plastic of the holes in the connector. The case parts have also texts "THIS SIDE UP" and "THIS SIDE DOWN", because great harm and smoke can occur if inserting a user port cart upside down.