Excavator Swing Bearing  is a rotational rolling-element bearing that typically supports a heavy but slow-turning or slow-oscillating load, often a horizontal platform such as a conventional crane, a swing yarder, or the wind-facing platform of a horizontal-axis windmill. (To "slew" means to turn without change of place.)Slewing bearings often use two rows of rolling elements. They often use three race elements, such as an inner ring and two outer ring "halves" that clamp together axially.Slewing bearings are often made with gear teeth integral with the inner or outer race, used to drive the platform relative to the base.