There is no comma at the end...
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You have to cut out the "D" shape hole with a Dremel and X-acto knife. I used the Dremel to open a small hole kinda offset to the center, then used the X-acto knife to cut in the flat edge oposite the offset. I cut mine a hair smaller, then used a metal axle pin and pushed it thru to open it up to the exact shape.
You may want to add some kind of spacer behind the wheels too depending on which set you are using.