Taper roller bearings consist of an inner ring (cone), an outer ring (cup), a cage and rollers which are profiled to distribute the load evenly. They have high radial and axial (thrust) load capacities at low to intermediate speeds. Taper roller bearings are available in single-row, two-row and four-row designs. With single-row bearings, the thrust load capacity is about 60% of the radial capacity. Double-row bearings have a greater radial load capacity and can handle thrust loads in both directions. The rollers can be configured in such a way that the contact lines between the roller and the race converge or diverge towards the axis of rotation. Diverging double-row bearings increase the rigidity of the shaft mounting, while converging bearings do not. Other configurations for double-row bearings feature a single outer ring and two inner rings, or two outer rings and a single inner ring. Four-row tapered roller bearings consist of four rows of alternating converging and diverging rollers.Most taper roller bearings are made of alloy steels or low-carbon steels. Some applications require the use of case-hardened or through-hardened, high-carbon, bearing-quality steel. High-carbon grades of steel do not require carburizing and can be case-hardened by induction heating or through-hardened by conventional heating methods. When low-carbon, carburized grades of steel are used, carbon is introduced after the cylindrical roller bearings are machined to a depth sufficient to produce a hardened case that can sustain bearing loads. The addition of carbon and alloys ensures the proper combination of a hard, fatigue-resistant case and a tough, ductile core.