This knob is designed to fit a D-shaped shaft as used for windshield wipers (without the washer button) and the fan control on a 1964 Valiant, and to resemble the factory knobs. It is designed in two pieces to eliminate overhangs and supports.
I simplified the dished steps in the center, and changed the fluting to work with Sketchup and my beginner-level work. There is no provision for a set screw, but it fits tightly enough on the D-shaft that one should not be necessary.
ABS should stand up to summer temperatures better. Be careful with bed adhesion.
I needed another knob for a vintage-style under dash air conditioning evaporator, to match the rest of the knobs on the dash. Nicely chromed metal reproductions are available, but it looked like a fun project to draw up and print..