This section is from the "A Complete Dictionary of Dry Goods" book, by George S. Cole. Also available from Amazon: A complete dictionary of dry goods and history of silk, cotton, linen, wool and other fibrous substances,: Including a full explanation of the modern processes ... together with various useful tables.
Diagonal. A term introduced in the United States in the year 1875 denoting a variety of worsteds used in the manufacture of men's fine clothing, especially for coats and vests ; it is twilled in such a manner that the diagonal ridges are somewhat prominent and noticable. The Supreme Court of the United States has decided that an importation of cloths known as "diagonals" was, under the law as it existed before the passage of the Worsted Law, dutiable at 24c. per pound and 35 per cent. advalorem, as "manufactures of worsted not otherwise provided for," and not at 35c. per pound and 35 per cent. as "manfuactures of wool". These goods are known to the trade as "worsteds", therefore they are held to be dutiable under the paragraph relating to "worsteds" regardless of the fact that they are wholly the product of wool.