Jumbo Chicken-Head Knob overlay

This is an extra-large pointer ("chicken head") style knob. I was afraid that mating the 3D-printed shape directly to a quarter-inch shaft wouldn't be strong enough, so this knob is an overlay for an existing commercial knob.

The original knob was one of these: https://www.sparkfun.com/products/9998

The "Basic knob cutout.stl" file is a plain 3D model of the bulk shape of the original knob, with no detailed features or shaft hole. The "Basic knob cutout with hole.stl" file is the same, but