Tappable Knob

This is a customizable knob, designed to be part of a featherboard or miter clamping system. Most of the knobs on Thingiverse are designed to be used with a press fit hex bolt, or to slip onto a bolt. I wanted one I could tap into, because drilling and tapping takes a lot less time than prototyping the correct size hex nut hole. A lot of the knobs on Thingiverse also have too many parameters - this one only has 6:
►knob diameter
►knob height
►shaft height (as a ratio of full height)
►number of grippy cutouts
►bolt diameter
►shaft resolution ($fn).

The following are algebraically calculated, so as to not be stupid:
►diameter of the grippy cutouts
►shaft diameter (calculated as the mean of twice the bolt diameter, and half the knob diameter)
►suggested filename (which doesn't render in the final part) - a nice feature when you are prototyping