The hub is the part of the wheel that holds the spokes and allows the wheel to rotate about the pinning axis.
How to choose a bushing?
Hubs or their parts are something that may fit one bike but not another. Although, of course, some of the details are universal. The hub is the part of the bike that is prone to wear and tear because it runs the longest.
At the moment, the evolutionary development of this node has led to an established standard form. The bushings are divided according to the type of brakes, respectively, there are bushings for a disc, rim, aka vibrake, and a foot brake. Pay attention to the type of bearing that is used in the bushing: cassette, industrial bearing or loose. Cassette and industrial bearings are much more convenient to use and easy to change. But bulk is much cheaper and has less sliding friction.
The second important hub element is the axle. It can withstand all loads, must carry the weight of everything on the bike, including the bike itself. Replacing a broken axle is a very painstaking work, therefore, when choosing a new axle for yourself — reinforced, regular or lightweight — check that its parameters coincide with the one that was before. Also note that the new hub matches the spoke capabilities of the rim.