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.
Knitting' Silk. A slack-twisted silk yarn, used for the knitting of hosiery and in the making of fancy articles. It is made of both "spun" silk and " reeled " silk. The latter is a strong and elastic thread or yarn, with a high degree of metallic luster. Spun silk being made from " waste," or imperfect cocoons that cannot be reeled, is carded and spun like cotton, hence the thread has a dead, lusterless appearance. Knitting silk comes wound in half-ounce balls, all colors, in two sizes - 300, coarse, and 500, fine. Each ball of No. 300 contains 150 yards of silk; No. 500 contains 250 yards; No. 300 is equivalent to size EE in embroidery silk.