The bearings come with ceramic rolling elements in a wide selection of steels, closures, mounting configurations, cages ( retainers), and lubricants. Preloading-radial or angular-contact bearings boost rigidity, improves running accuracy, and prevents ball skidding at high speeds and during acceleration and deceleration. Kaydon Bearings Div., 2860 McCracken St., Box 688, Muskegon, MI 49443, (800) 514-3066, kaydonbearings.com