6 X 37 CLASSIFICATION Because of emphasis on fatigue resistance the problem of choice within the 6 x 37 Classification is greatly reduced. Although there are exceptions, the constructions in the 6 x 37 Classification 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 two inches, the 6 x 49 SWS construction is normally used. In smaller sizes, however, the outer wires in the 6 x 49 SWS would be so small that their resistance to abrasion would be lowered. It should be noted that the greater number of wires make the 6 x 37 classification more susceptible to crushing. This, however, can frequently be overcome by an independent wire rope core and by the use of well designed sheaves and grooved drums.