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.
Embroidery Silk. The fancy colors are usually put up 10 yards to a spool, each spool being equal to four ordinary cards or skeins. All colors except black and white are EE in size (equal to No. 300 in knitting silk). Black and white are made in four sizes, E, EE, F, FF, from fine to coarse in the order named.