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.
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.