hat are the categories of bicycle hubs

The hubs of bicycles, that is, the front and rear axles, can be roughly classified in the following ways: according to the type of bearing, according to the width of the gear opening, according to the size of the shaft core, according to the type of the freewheel, and according to the type of brake:
According to the type of bearing (bead block type, bearing type):

The bead-blocking hub is a bearing structure in which loose beads are placed inside the hub and supported by a shaft block. Currently, the most famous brand that uses a bead-blocking hub is Japan's Shimano. The biggest advantage of the bead block hub is that it has good support for the force from all directions, but the disadvantage is that the maintenance is slightly cumbersome.
Bearing hubs and hubs with integrated industrial bearings are currently used by most brands. The longitudinal force of the bearing hubs is relatively reliable and the maintenance is relatively convenient.
By opening width:

The opening width is the frame and front fork opening size that can be supported by the shaft core length of the hub. Generally speaking, the opening of the front hub is 100mm; Between 130mm; mountain bike rear hub opening is between 135-150mm.
According to the shaft core specification:

The shaft core is divided into ordinary shaft core and barrel shaft. The common axle core and the hub are connected as a whole. Generally, the front hub is 9mm in diameter and the rear hub is 10mm in diameter.
The axle core of the thru-axle hub is separated from the hub body, and the diameter of the axle core is generally 10mm, 12mm, 15mm, and 20mm. Thicker thru-axles are mostly used for high-intensity sports bikes, such as all-terrain mountain bikes, downhill bikes, and more.
By freewheel type:

The freewheel base is the base on which the flywheel is installed, and there are two types of threaded rotary freewheel base and cassette freewheel base.
By brake type:

The hub that can install disc brake pads is called disc brake hub, and the disc has two installation methods: central locking and six-pin.

Non-disc hubs do not come with disc brake mounts.
By lock type:

A hub that can be locked with a quick-release lever is called a quick-release hub, while a non-quick-release hub is locked with a nut.