One of my friends could not find any replacement valve (knob) for his radiator and ask me to make a "funny" one ("coloured if possible"). I didn't find on thingiverse the exact size and shape that fit the original part, so I decided to design one. After creating it, I was trying to put the "+/-" symbols on top (to explain how to turn it to increase or decrease heat), and I found that it could be drawn as a smile (sort of clown face). I like it as is.You don't need to print it with 100% infill (30% infill with 3 perimeters and 3 top/bottom layers is strong enough I guess)