35 Inch Four-Point Contact 878x1185.6x100 mm Ball Slewing Ring Bearing with Outside Gear35 Inch Four Point Contact 878x1185. 6x100 mm Ball Slewing Ring Bearing with Outside Gear Four Point Contact Ball Slewing Bearing with Outside Gear A slewing bearing 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, or the wind facing platform of a horizontal axis windmill. (To 'slew' means to turn without change of place.)