I would have said use a smaller bolt and a separate nut but having seen the shape of the reference body it looks like there's no way of fixing a nut. Perhaps you could try using the next size up bolt and cutting a new thread? Of course this may destroy the cartridge and risk your headshell as well ... remind me to avoid cartridges that won't take a nut 😏
Using a larger bolt is a recipe for disaster. Try wrapping some plumbers tape over the bolt - this may be enough to get some purchase on the thread. Alternately, why not send the cartridge to someone like Soundsmith to effect a proper repair. Should not be a costly repair.
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