There is no 8.33mm thread. Are you measuring the thread or a stepped down end? You said a 9x26 cone fit, was it radially sloppy or a decent fit.
If the 9x26 cone fit then that's what you need. Maybe you also to check your caliper. Measure a 6mm hex key across the flats to check. It should be between 5.96 and 6mm.
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