My Staco 3PN1010 variac knob was broken so I modeled up a clone replacement. I designed it to be a tight fit on the shaft. It uses 2 set screws to secure the knob. I purchased M4x0.7 24mm long set screws. If you have a tap for the existing thread the hole should work fine.

Print Settings
Nozzle: 0.4mm
Layer Height: 0.2mm (variable layer height was enabled on the top curve)
Infill: 30% Gyroid
Ironing is recommended
Multicolor recommended (white line)

I included a Bambu Labs .3mf file with the slicing settings already completed.