The 6*7+Iws classification of wire rope includes most 6 strand , round strand ropes having 27 to 49 wires per strand. While 6 x 19 ropes give primary emphasis to abrasion resistance in varying degrees, the 6 x 37 ropes are important for their fatigue resistance. This fatigue resistance is made possible by the greater number of small wires per strand. Because of this emphasis on fatigue resistance the problem of choice within the 6 x 37 classification is greatly reduced. Although there are exceptions for special applications, the constructions in the 6 x 37 classifications are primarily designed to be the most efficient for each rope diameter. As the rope size increases, for instance, a large number of wires can be used to achieve required fatigue resistance and still those wires will be large enough to offer adequate resistance to abrasion. In sizes over 2 inches the 6 x 49 SWS would be so small that their resistance to abrasion would be a problem.

It should be noted that the greater number of wires makes the
6 x 37 classification more susceptible to crushing. This however,
can frequently be overcome by an independent wire rope core
and the use of well designed sheaves and grooved drums