assembly containing the spindle (or axle) as well as its bearings, as opposed to them being separate parts which must be mounted separately. Cartridge hence refers to the functional assembly unit, and does not indicate what type of bearings the cartridge utilizes. Either loose ball bearings (adjustable cup and cones), sealed bearings or other types of bearings may be used in a cartridge assembly. Independent of the type of bearing used, the cartridge often has some sealing to protect the assembly from the environment.

Sealed cartridge