Hi

For what it is worth I think that drilling a hole down the centre may be a very bad idea. Think about it, the Chinese are very good at making things down to a price so their design is not going to be conservative, that's for sure. Therefore, the diameter of the shaft will have been minimised in diameter and material specification to do the job and no more. Removing some of this material will weaken the structure I am sure.

If you want to do it anyway and can't drill or bore it because the material is hard, you can always get is spark eroded ....maybe.

Still think it is not a good idea though.....sorry