Industrial truck mast guide ball bearings are a family of special bearings tailored to meet application requirements. These bearings must be able to accommodate heavy radial loads, withstand heavy shock loads, and handle overturning moments produced by combined radial and thrust loads. Special lubricants are selected to meet the rigorous demands of industrial truck service. To retain the lubricant and protect the bearing from adverse environmental conditions, the bearings are equipped with either synthetic rubber or polypropylene seals.