Slewing rings are one of the most important parts of cranes. The slewing ring provides the crane with its possibility to rotate while lifting loads. Naturally, slew ring has to be in good shape for the crane to fully function.A slewing bearing or slew[ing] ring 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.)