They're likely stripped out, that happens a lot with these cars' lugs due to the cheap plastic used , they will just strip out inside. If you don't have new wheel nuts ... you can order aluminum or other kinds online. One of the best ones I have found is through Atomicmods.com..
link to their wheels / tires section
You can also use the Kyosho Mini-Z packages as well..
click
And yeah, I used to be pretty into xmods.. I'll post a thread with my pics so I don't hijack yours
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I'm on a boat