I have successfully glued up African Blackwood to a variety of other woods and internal 'rods' by first degreasing the surface with IPA or cellulose thinners and then using either epoxy or superglue.
While the application was slightly different - the bonds usually held up during further turning.
To bond 8mm threaded rod into Blackwood I would suggest that you have two methods available to you:
Firstly, when you drill your hole for your threaded rod, form a 'keying' slot on the inside of the bore hole. I simply use a threading recess tool (borrowed out of the tub that holds my thread chasers), and use the back corner to form a 'v' or 'U' groove about 6mm inside the hole. This tool fits into an 8mm hole quite easily (was using it today for the same purpose). This provides a kind of 'locking ring' which helps to hold the epoxy in place once it has set. The threads on the rod will serve the same purpose. First degrease the wood well, immediately prior to glue up, do glue straight away after the degreasing agent has evaporated.
Secondly, you could drill and tap your hole to suit your threaded rod. African Blackwood takes a thread very easily, and I have seen items made a 100 years ago that were threaded up and still good. If you then wash your threaded hole with IPA/cellulose thinners, squeeze some araldite/epoxy resin into the hole and screw in your threaded rod, it should stay there for generations.
One thing I have learned from experience is that when you glue a rod into a handle or shaft of a walking stick (or anything else for that matter), it makes life a lot easier if you first drill a 0.5mm 'Dribble Hole' just above the bottom of your hole. This allows excess glue to escape during glue up, is easy to clean off, and no pressure is required to keep the parts together while they cure. It's an age-old technique used in woodworking to prevent the mortises from cracking when the adhesive dries and expands.
I hope this helps.
ps. I tend to make the hole a little deeper. I usually use a 50mm deep bore with 8mm rod.
