Generally, slewing bearings are large-size rolling bearings that can accommodate axial, radial and moment loads acting either singly or in combination and in any direction. They can perform both slewing (oscillating) movements as well as rotational movements. Basically, a slewing bearing consists of an inner ring (a), an outer ring (b) and rolling elements − balls (c) or cylindrical rollers − that are separated by polyamide spacers (d). The rings, one of which usually incorporates a gear (e), are provided with holes (f) to accommodate attachment bolts. The holes may be threaded. Generally, only the raceways in the rings (h) are hardened and precision- ground. Integral seals (g) made of acrylonitrile- butadiene rubber (NBR) keep the lubricant in, and contaminants out of the bearing. Slewing bearings are relubricated Slewing bearings through grease fittings (i) to reduce maintenance and operating costs.