Full disclosure: this has not been printed
A familiar valve style machine head tuner button (knob).
I'm concerned that it may be too delicate at this size for use especially considering how tight it is in the shaft. (The shaft hole has been used in other models by me).
These are the tuners I was basing the shaft profile on:
Kmise A1966 Acoustic Guitar Tuning Key
Though it does seem to be pretty common.
Found a better source and added a much better looking and stronger version. Relisted as a remix of that source.