a contract concluded by an undertaking (hereinafter called the'principal contractor') with another undertaking (hereinafter called the'subcontractor') under which it is agreed that, in performance of another contract made between the principal contractor and a third undertaking (hereinafter called the'buyer'), the subcontractor will deliver goods or perform services which the principal contractor must incorporate or use in supplying the item or items which the buyer has ordered from him, it being understood that: (a) Position in law The subcontractor is not a co-signatory to the contract concluded between the principal contractor and the buyer, and the principal contractor has sole responsibility to the buyer for performance of the contract and bears all the risks which may be guaranteed in relation to the latter. (b) Technical and economic position Supplies from the subcontractor cover goods (other than raw materials or semi-finished goods) and/or services which, from the technical and economic point of view, consitute for the buyer essential ancillaries to performance of the contract by the principal contractor