Full definition
Precision machine element supporting a rotating shaft while minimizing friction between moving and stationary parts. Rolling-element types: deep-groove ball (most common, radial + light axial), angular-contact ball (combined loads), cylindrical roller (heavy radial), tapered roller (combined heavy loads), spherical roller (self-aligning, misalignment-tolerant), and needle (compact, oscillating). Standardized per ISO 15 (dimensions), ISO 281 (load ratings and life calculation), ISO 492 (tolerances: P0, P6, P5, P4). Basic rating life L10 = (C/P)^p × 10^6 revolutions, where C is dynamic capacity and p = 3 (ball) or 10/3 (roller). Lubrication: grease (sealed or shielded, most maintenance-free) or oil (high speed). Brands: SKF, NSK, NTN, Timken, FAG (Schaeffler), Koyo (JTEKT). Proper mounting, lubrication, and contamination protection are the top three factors determining actual service life.