A housing for a round rocker switch. You can see the dimensions of the switch in the photos.

I haven't bothered with a back plate because it's designed to be screwed into the wall.

Have added:

4mm Diameter cable version:

• Inline cable holes
• Side cable holes

5mm Diameter cable version:

• Inline cable holes
• Side cable holes

Print with supports.

I've printed mine in PLA, with four perimeters and 15% infill and it's really sturdy.