GTR and 350Z rotors actually fit the 300zx hub including centerbore and lug diameter. Cobra rotors do not fit the 300zx hub correctly, the hub bore is different (this is fixed with a hubcentric ring) and the Cobra uses larger lugs. The Cobra rotor has some play because they should be used with 1/2" (12.7mm) lugs, not 12mm that the 300zx has.