The original axles used a simple bearing system. I would like to change this to a ball bearing system because the stock design has lots of friction related drag.

 

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Pictures on the left show the axle assembled with the plastic piece in place that holds the wheel from slipping on the axle. Picture on the right shows the plastic piece removed, the nut that it is held in place by, and the back side of the plastic peice.
All pictures show where I would like the ball bearings to mount. The original bearings in desired position and are about half at thick as the ball bearings, so the axle needs to be thinner in those areas. Similar to the threaded sections on the end. The axles are actually able to be reduced to this diameter except for where the "nut" and the plastic "c-clips" are.
Short Axle
Short Axle
Large Axle
Large Axle

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