I had a problem with 3D printed knobs, they are either too tight or too loose.
If you use a small clearance and inaccuracy (especially in corners) makes the knob pretty much impossible to use without filling, a larger clearance and the knob is too loose - there seem to be no happy middle ground.
This design solves this problem by changing the connector - instead of a solid knob with an hole there's a hollow knob with thin "flaps" that are too tight but are flexible so they fit anyway and small holes where the corners are supposed to be so corner over-extrusion isn't an issue.
Designed for a 0.4mm nozzle, you can use whatever infill percentage you want because the important parts are all walls.
Designed with Autodesk Fusion 360, Printed on Robo3D R1+