These knobs fit on the vent door bracket on a Van's Aircraft RV-12. The knob provides an easy way to adjust the door for airflow. The knob has a cut to accommodate bracket angle when the door is fully open.  Use the RV-12is KAI section 23is-U08 for installation instructions. 

Installation requires matching drilling the bracket with a hole to pass the attachment screw. It is helpful to tap the screw hole with a 4-44 or M4 tap and a matching screw.  A ½" long (12mm) screw length fits perfectly.  

If you have a multi-material printer, the left and right production set with TEXT file can be used. It was created with PrusaSlicer 2.4.2. The text color is inset for the first three layers (print face down).