The question of what if any protection should be given to manufacturers of composite products against the production and sale of spare parts for use in such products is a vexing one that has frequently come before the courts in many countries in recent years. Most frequently it arises in connection with spare parts for cars. The car manufacturers wish to prevent sales of anything other than authorized spare parts. The insurance industry wishes to be able to obtain spare parts from the cheapest possible source.

The most recent round in the fight was fought in the Bilbao Appeal Court in Spain in the case of Ford Werke AG v. Construcciones Metálicas Arregui SA. Ford owned international design registrations for the front fenders and hood of a car. The defendants produced spare parts which were exact reproductions of the registered designs. Ford sued for infringement of the designs and for unfair competition. The appeal court rejected both claims. The design for only part of the article that should have been protected (the car itself) was invalid. The court commented "the [part] made for a particular vehicle ... serves only the function to which it is destined and by itself is useless and does not bring any enrichment to the patrimony of the forms applicable to industrial products". Since under national law parts were not protectible, no additional protection could arise simply because the design was registered under an international convention. So far as the unfair competition claim was concerned, the defendant made clear to purchasers that the parts in question were not made by Ford. This caveat was sufficient to result in a finding for the defendant.