The hub is the core of a wheel, since it’s where the spokes sit from the rim while staying bolted to the frame and allowing the free rotation of the wheel.

Key points:

· Axle spacing: in 20” bikes, it’s usually 110mm (when using snail cams) or 116mm (with integrated or sprung chain tensioners). In 26” bikes, apart from the aforementioned dimensions, 129mm (with snail cams) or 135mm (with integrated or sprung chain tensioners) are also common.

· Axle diameter: 10mm in most cases.

· Spoke holes: usually 32 holes (32H), although some older models have 36 holes (36H).

· Rotor mounts: a rear hub might or might not have standard 6-bolt rotor mounts.

· Bearings: sealed bearings are more reliable and durable than open bearings.

· Sprocket interface: it can be threaded (standard 1.37” x 24tpi thread) or splined (Shimano HG, Echo, etc.).