Hint 2: Most spinner knobs, like the ones for Ultimarc's Spintrak, fit a 1/4" (6mm) shaft, but you may need to measure where the LEDs are if you got the illuminated Atari knob version.

Alternate method -- measure after you get it.
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This Atari spinner from Happ is out of production, but available at Arcadeworld UK.
It is also sold as Tornado Spinner.
Note that the led PCB at the sales pictures is mounted wrong. The leds must be shine down, not up.
That's why the knob tube is clear pastic.
And Only then you can use a about 12 mm hole for the Spinner axle.