Replica Piper Heat Duct Knob (66980-00)

thingiverse

This is an exact replica of the knobs used in Piper Cherokee aircraft for Cabin Heat and Defroster control levers, heat duct levers, and alternate air control on fuel-injected engines. The final printed result matches the original width at the base. The fit is excellent. The round hole must be tapped with #8-32 threads, and a #8-32 set screw should be used. I recommend using set screws that are 1/4" long with a cup point. Using set screws that are 3/16" long with a cone point will also work, but 1/4" would probably be better. The original screws had a cup point, so reusing them should work even better if you have the original set screws from your old cracked knobs.