This is a key cap set I worked up for my Dactyl Manu-Ball keyboard project: https://www.thingiverse.com/thing:4306733

The shank or shaft is designed to fill the space with as much material as possible to give the cap a real solid connection to the switch.

I printed my set with ColorFac XT-CF20 which is a tricky material to print with. I also over extruded the white by 10% so ensure it filled the area between the black more completely

ToDo: Chamfor corners around face of cap.