Shock absorber cord is made from natural rubber strands encased in a braided cover of woven cotton cords treated to resist oxidation and wear. Great tension and elongation are obtained by weaving the jacket upon the bundle of rubber strands while they are stretched about three times their original length.
There are two types of elastic shock absorbing cord. Type I is a straight cord, and type II is a continuous ring, known as a "bungee." The advantages of the type II cord are that they are easily and quickly replaced and do not have to be secured by stretching and whipping. Shock cord is available in standard diameters from 1/4 inch to 13/16 inch.
Three colored threads are braided into the outer cover for the entire length of the cord. Two of these threads are of the same color and represent the year of manufacture; the third thread, a different color, represents the quarter of the year in which the cord was made. The code covers a 5 year period and then repeats itself. This makes it easy to figure forward or backward from the years shown in figure 6-55.