This simple case consists of two parts:

• a top part featuring a 7mm hole on its top face to fit a potentiometer (this type) and another 12mm hole on its side to fit a 2.1mm barrel plug (this one). There is also two 1.5 mm holes on the other side to let cables out to be plugged on whatever you need to dim.
• a bottom part, to enclose all the electronics.

The two parts of the case are assembled using 2 M2 screws with their nuts. 5 mm long screws fit perfectly. I use this box as a dimmer for a LED strip (you can find the case I designed for this strip here). If your use case is similar, I would suggest buying a combined potentiometer/switch.

If this case does not fit exactly your need, feel free to change its dimensions using the provided step file, or by duplicating my original document in Onshape.