Recommended for heavy loads in moderately dirty environments. Rubber contact seals protect against dirt and debris but may be damaged by overly abrasive materials. A hole through the inner race allows the bearing to be regreased through the axle. Bearings that are regularly regreased can withstand very high levels of debris without damage. The seals add rotational drag and are not recommended for gravity applications with light product. Recommended for powered applications where roller resistance is not an issue and the roller is constantly rotating.