http://imgur.com/6orZXtp - The green spacer 12 holes.
http://imgur.com/TskU7rT - wheel with 6 holes.
We will probably change it over to 6 single bolts going all the way through there was a really good reason we did not do this in the first place and now i cant remember why.
For gears steel on steel i think is what we will run for the initial prototype types.