The shaft of the light dimmer button knob at my father in law's was broken:

So I made him a new one! It is meant to fit a 4mm stem, the build plate contains 2 variants 1 a bit deeper and one a bit more shallow. But you can make the sizes as you wish using MakerWorlds “Customize” feature.

Because of the slight tapering of the shaft the cap fits really tight to the stem of the dimmer. This model works perfectly (see picture), so if you are in need of a dimmer knob too, you might try this one.

New: Customizable with the Parametric Model Maker!

Now you can use the MakerWorld Customize option to set your own stem diameter + shaft length and knob diameter and depth to perfectly fit the model to your needs 🎉 Look for this button above: