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Drill a hole slightly larger than 10mm and epoxy the threaded rod in would be a 'professional' approach. By that I mean likely to last long enough without having to understand the really long term effects on the wood of the epoxy+threaded rod.
If you drilled a 9mm hole you could probably get the threaded rod to thread into it with a couple of temporary nuts in place.
I would only drill part way into the post. It's kind of tricky to drill into the end of a rod as you can't fit it in a pillar drill. Fortunately you can bend the rod to straighten the post once it's in place.
Dredging this post to ask how you would fix the threaded rod if they weren't already done? I could potentially get a chippy round the corner to drill some holes all the way through as mine will only be about 600mm but is an access hole in the side to tighten a nut usual method, or threaded insert a better bet?