Korg Wavestate, Opsix  Rotary Encoder Knob, 510646800239

There is 1 of these on the wavestate.

510646803115, White Knob, 8 on Wavestate

510646803116, Black Knob, 16 on Wavestate

Top Diameter 13mm

Bottom Diameter  13.5 mm

Height  16 mm

D shaft  6 mm