I needed an enclosure for a small prototype PCB I had made, like this:
In the description of the PCB, it is said to be 50x70 mm, but it actually is 51x71 mm, and that is what this box is designed for.
The PCB slide in via a slot on each side of the inclosure, and sits quite snug. There is 4 mm space underneath the PCB, whis is plenty for pins and wiring, and 18 mm on top of the PCB, whis is enough for an arduino nano (or micro, nodemcu, etc) mounted in a pin header.
I designed three different boxes and three different lids. The only differenec between the boxes is the amout of ventilation holes. The difference between the three lids is one does not have any holes, one a one slot/grove that allows for some cables, and the last one has a hole for a usb connector to an arduino (e.g.), if the arduino is mounte on the pin header.
I printed the boxes standing on the high edge. That way I didn't need any support.