NKE’s modular bearing system for planetary gears in wind turbine gearboxes consists of cylindrical roller bearings that are fitted directly into the planetary gear, the bore of the gear acting as the outer raceway. Developed to customer specifications, the system has been applied in projects using gearboxes rated 1.5 mW, 2 mW and 2.5 mW, for example, with single-row cylindrical roller bearings without an outer race. The bearings have bore diameters of 160 mm, 190 mm and 200 mm and are fitted with an inner-race-guided, one-piece brass cage, which contains inspection grooves for endoscopic condition assessment of the inner race surface. For higher loads and wider gears, they can be assembled to form sets of two, three or four bearings.