The use of proper names, trademarks or trade names or similar words to refer to materials or articles is undesirable insofar as such words merely denote origin or where they may relate to a range of different products. If such a word is used, then, where it is necessary in order to satisfy the requirements of Art. 83, the product must be sufficiently identified, without reliance upon the word, to enable the invention to be carried out by the skilled person at the date of filing. However, where such words have become internationally accepted as standard descriptive terms and have acquired a precise meaning (e.g. "Bowden" cable, "Belleville" washer, "Panhard" rod, "teflon" layer, "caterpillar" belt) they may be allowed without further identification of the product to which they relate.