[DonRotolo]

Screwing a plastic hub to a COTS item doesn't make the COTS item non-COTS, does it? Kinda like using a clamp to hold a broomstick, the broomstick is still COTS.

Of course, the OP seems to be replacing the hubs with plastic bits; this makes it non-COTS (unless the tire is available separately, which remains COTS then)