A project I've been thinking about for a long time... A standard button for "Schneider Trend" (formerly known as "Eljo Trend") wall switches. They're very common in Sweden, and now you can print your own buttons for it. Maybe in some exciting color?

I made the 3D model using nothing but an original switch button and a vernier caliper. I've tried printing one, and it works! Needed a little polish on the two "pins" underneath. They need to be thin enough to slide into the switch mechanism.