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.
Line. In button manufacture, one-fortieth of an inch; the size of buttons being denoted by the number of lines across the diameter. Thus a 22-line button equals twenty-two-fortieths of an inch from side to side; an 18-line, eighteen-fortieths of an inch, etc. The term is also used in indicating the width of braids, etc., having reference to the number of ribs or plaits in the width.