The systems used for fiber glass yarn product nomenclature are the Inch-Pound version or the TEX/Metric version. TEX is the mass in grams per one thousand meters (g/1000 m) of length. The Inch-Pound yardage is the bare glass yardage in a single pound of strand. 

   A typical yarn desc ription would be as follows:
   U.S.-ECD 450 1/0 1.0Z
   S.I.-EC5 11 1 x 0 Z40
   These systems of identification use both letters and numbers to describe the product.
  
   The Letters
   In the above examples, the first letter, "E", indicates an electrical type glass composition. Although this composition was originally formulated for electrical insulation applications, this composition is now used broadly in most fiber glass yarn applications. The second letter, "C", indicates continuous filaments combined into a single strand. Use of the letter "T" as the second character indicates that the product is texturized. The third letter in the U.S. version, "D", indicates the nominal diameter of the filaments forming the strand. The U.S. version expresses this diameter in inches (see the Ordering by TEX table on the next page). The third character in the S.I. version, "5" indicates the nominal filament diameter in microns.
  
   The Numbers
   The first group of numbers in the U.S. example (450) represents 1/100 of the total approximate number of yards in a single pound of strand. This is known as the strand count.
  
   Example - ECD 450
   450 x 100 = 45,000 yards/pound
  
   The first group of numbers in the S.I. example (11), indicates the TEX (grams per 1000 meters) of the strand.
  
   The next set of numbers (1/0 or 1 x 0) reveals the number of basic strands in the yarn. The first digit of the series expresses the number of strands twisted together in making the yarn. The second digit, which is separated by either the diagonal or a lower case "x", indicates the number of twisted strands that have been plied together to form the final product. PPG does not manufacture plied yarn products, so the second digit will always be "0" for any KTYU yarn product.
  
   The Twist
   The final set of numbers and letters indicates the amount of twist and the direction of twist in the final strand. The numbers (1.0 or 40) indicate the turns of twist per inch (U.S.) or per meter (S.I.). Yarn has S-twist if, when the yarn is held in a vertical position, the visible spirals or helices around its central axis conform in the direction of the slope of the central position of the letter "S". Yarn has Z-twist, if the visible spirals or helices conform in the direction of the slope of the central portion of the letter "Z".
  
   In S-twist, the strands assume the ascending right to left configuration, as in the central portion of the letter "S".
  
   In Z-twist, the strands assume the ascending left to right configuration, as in the central portion of the letter "Z". 
    

Yarn Industry

The TEX identification used by FIBTEX is based on the nominal bare glass
 yardage of the basic strand ordered. The TEX number is then rounded off as recommended  by ASTM D-578.