Four-Bolt, Round Cartridge - Medium Duty Four-Bolt Medium Duty Flange Bearing Unit Application Four-Bolt Medium Duty Flange Cartridge Bearings may be found in a variety of applications, including, but not limited to, agricultural equipment. Benefits using Flange Cartridge Bearing Units Flange Cartridge Bearings may be installed in equipment in cartridge form (i.e. installed within a housing/machine area) and are also suitable for surface mount installation (similar to square Flange Bearings). The Medium Duty models are suitable for heavier duty applications where Normal Duty models would otherwise be used.