Adjustment nut knob (parametric)

I have a big floor fan that constantly tipped toward the ceiling because the adjustment nuts on it were loose. It came with knobs, so the nuts could be tightened by hand, but those knobs fell off and got lost. So now, new knobs!

Hopefully I correctly understand what "parametric" means. The .scad file contains a single module call whose parameters can be adjusted to change the size and shape of the knob. If I misunderstood the point there, go easy on me, as this is my first Thing! Hope yo