Unfortunately the gear center is hollowed out to allow for a ratchet system, so there is no center and the hollow isn't even a circle!

This is why I either need to find a new gear altogether that I can attach to the drill, or someway of affixing it.

The blue wheels from robo challenge have those nut inserts, if I could get a hold of one of those inserts then I should be able to mount that inside the gear..........

Alternatively if your sure of the thread type then I could try and somehow fill the empty space (any ideas how?) and tap a thread.