and this is a video of the wheel replacement. i hope this helps
https://www.youtube.com/watch?v=UrWy-eliBes
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EDIT: the wheels probably fell back off because from the pictures on the replacement parts site has loctite blue on the bolt itself to keep it from backing out.
please see attached links.
one is replacement parts for the ripstick
https://www.ereplacementparts.com/razor-ripstik-skateboard-parts-c-194165_194171_194200.html
and this is a video of the wheel replacement. i hope this helps
https://www.youtube.com/watch?v=UrWy-eliBes