The most commonly replaced parts in a hub are the hub bearings and freehub bodies. The bearings usually require replacement due to wear and tear, as these parts are expected to wear out eventually through normal use. Sometimes these hub bearings are bundled together in a pack from the manufacturers, which can be found above, and sometimes they need to be purchased separately. This can be done by reading the code off the bearing seal to identify it, and then they can be purchased here. Some of the manufacturer's kits also contain freehub bodies, which can need replacing if they become damaged from a cassette being too loose, leaving indentations in the freehub body. These freehubs can also often be purchased separately and usually contain a set of fresh bearings inside them.