Illegal lug-nuts, are they nuts?

I kept hearing on Saturdays Bush race that 2 cars were penalized for having illegal lugnuts. I hane not heard anything else on this. Does anyone know what they were refering to?? I really want to know. I have searched all over the Nascar.com page, yahoo and several other pages with no reference to the "illegal" lugnuts. As long as they were holding the tire on...whats the problem?