A friend needed a macro pad with three keys, as small and simple as possible. No fancy rgb, no colors - just a plain small macro pad.

So I made one, inspired by Stream Cheap by @dmadison_238071.

Parts needed:

• 2x M3x8 screws
• 3x Cherry MX keys (or others, I don't know if they fit)
• 1x Pro Micro module with USB-C (read below)

• Some wires

   

Instructions:

• Print everything in your favorite material
• Place the keys into the panel
• Solder wires to one pin of each key to GND and bridge them, so they're connected
• Solder wires to the other pin and those ends to the pins 2, 3 and 4 of the Pro Micro
• Use some all purpose glue to secure the pro micro (also read below)
• Screw the panel to the case (the screws will cut threads on their own, it will be quite stiff)
• Copy my code to your desired IDE (I prefer Arduino IDE)
• Modify the key bindings on top of the code (key code list is linked there)
• Set device to “Arduino Leonardo” and flash it

Below:
There are several Pro Micros out there. I used this one. Others might have other dimensions. My Pro Micro snapped right into the case (on the photos you see that I've shortened it a bit, but this was just for a prototype, I've missed to make a photo of the final case).

The code for the Pro Micro is attached. Open the file with your IDE and change the keycodes on top of the code.
The macro pad is oriented, that the USB port is on the right. So the keys 2, 3, 4 are from left to right then.
If you use Arduino IDE, choose “Arduino Leonardo” as device. It'll work fine.
Also other ATmega32u4 should work but I'm not sure.