Hello,
I represent Team 1748; if anyone can help us. We are trying to mount a CIM motor directly onto the wheels.
We would be of great appreciation if you can help us out.
Andymark sells keyed hubs.
http://www.andymark.com/Hubs-s/215.htm
Just look for the right size for your wheels, and the key in the CIM.
This little guy makes it easy: http://www.andymark.com/product-p/am-0320.htm
I hope this is for some sort of scoring mechanism and not the drive… Direct CIM drive is not the best idea in the world…
its for scoring not for driving but THANKS 
Could you use 2 short pieces of reinforced rubber tubing from an auto-parts store? One piece fits the CIM shaft, the other fits the wheel axle (live axle), and the 2 are connected with a tubing adapter.
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We also had this issue a few weeks ago. We actually didn’t use either of the key hubs; rather, we bought the andymark 250 hub (.25 inch hole). We drilled the hole open just so it fit onto the shaft (.313" or so?). We then added a set screw on the side. Hammered it on and it works perfectly. Note that for the kop wheels you’ll be fine, but the plaction wheels need special fasteners (to attach to the hub).
8 millimeters