Freehub Body

The freehub body is the splined part of the rear hub that the cassette slides onto. It contains the ratcheting mechanism that lets the wheel coast forward without driving the chain.

Different drivetrain ecosystems use different freehub standards, including:

• Shimano HG — long-standing standard for 8/9/10/11-speed Shimano cassettes.
• Shimano Micro Spline — newer 12-speed Shimano MTB standard.
• SRAM XD / XDR — for SRAM cassettes that start at 10t.
• Campagnolo — Campagnolo-specific spline pattern.

When buying a wheelset, the freehub body must match your cassette. Many hubs allow the freehub body to be swapped between standards, but not all — check before buying.