This is a generic customizable knob with a lot of options (and not a lot of error checking so don't change too much at once). Multiple types of shafts can be accommodated including: circle, circle with internal or external keyway, D (partial circle), and any polygon (triangle, square, etc.). There is a test option to generate a simple disc with the specified hole/shaft pattern and mark angle for test fitting prior to printing the full model. The "standard" stl is based on a knob for an old heater that broke.

Edited .scad file to be more user friendly especially with the customizer and decreased the default $fn to 30 for quicker rendering, but you can always increase it if you want. Also, the rounded top feature was turned off by default to speed rendering.