This is a case for the Infrared Sensor 'Flying Fish,' which is used as an obstacle sensor in robotics or can also be employed to build a precise DIY tachometer, as demonstrated here: https://www.youtube.com/watch?v=6QZMt4yyylU
Since the sensor requires 3 wires, I find the use of a stereo audio cable for connecting the sensor ideal. Therefore, a 3.5mm stereo jack socket can be installed in the case. The two case parts snap together. For a sturdy connection, I recommend using an M2x4x3.2mm threaded insert and an M2x8 screw.
The author marked this model as their own original creation.