I moved into a house with two missing knobs for sliding light switches, so I made them.

Instructions

If your light switches are exactly like mine (and who knows, perhaps they're standardized), print the STL and stick the knobs on. My "prongs" were 2mm wide, 6 mm tall, and stick into the knob 12mm, and have little 'dents' to hold the knob on that are 6.5mm from the end. The knobs are 46mm wide, because that's the distance between the two light switches.

If your light switches don't match those measurements, put the measurements of your prong into the OpenSCAD script and generate your own knobs! Heck, if you have lots of knobs, add labels to them!

The script can generate knobs that are rectangular, cylinders, or spheres.The rectangular knobs are easiest to print; the other shapes require support. Print them with the hole for the prong down (that's how they're generated) so that the nicest side will be out into the room.

Apologies for the marginal photo. It's late, I'm tired. :-)