Customizable Stepper/Extruder Knob

A parametric recreation of Jeff Latham's Printrbot Feed Wheel. It's basically a knob that presses onto the tip of a stepper motor's flat shaft. Makes it easier to observe the extruder's motion and gives you the option of manually rotating the shaft if need be.
All the dimensions are adjustable - handle size, shaft length, etc. Depending on the design of your printer, you may need to make changes to avoid mechanical interference. For instance, the version I printed is sized to stick out far eno