What is the difference between Shimano HG, SRAM XD/XDR and Micro Spline freehubs?
By Crankworthy · Published · Updated
They are three different freehub bodies — the splined part of the rear hub the cassette mounts on — and a cassette only fits the one it was made for. HG is the long-standing Shimano standard with an 11-tooth smallest cog; SRAM XD/XDR and Shimano Micro Spline were created so the smallest cog could be 10 teeth.
How they differ
The freehub body decides which cassettes your wheel can take. It is the most common reason an otherwise sensible cassette upgrade does not fit, because it is part of the wheel rather than the drivetrain.
HG (Hyperglide) is the original Shimano spline, used by most 8- to 11-speed cassettes and by a few 12-speed cassettes designed for it. The cassette slides onto the splines and a lockring holds it on. Its diameter puts a floor on the smallest cog: 11 teeth.
SRAM XD drops that floor. The cassette threads onto a smaller-diameter driver, with no lockring, so it can start at 10 teeth. XDR is the road version, 1.85mm longer; an XD cassette fits an XDR driver with a spacer, but not the other way round.
Micro Spline is Shimano's answer for its 12-speed mountain groupsets. It uses many fine splines and also allows a 10-tooth cog, but it is its own standard: an XD cassette will not fit a Micro Spline driver, or vice versa.
Because the freehub is a separate, replaceable part on many hubs, switching standards is often a driver-body swap rather than a new wheel — but only if your hub's maker offers the body you need.
How to tell which one you have
- HG
- A splined lockring in the centre of the cassette, and a smallest cog of 11 teeth or more.
- SRAM XD / XDR
- No lockring — the cassette threads on as one piece — and a 10-tooth smallest cog.
- Shimano Micro Spline
- A Shimano 12-speed mountain cassette with a 10-tooth smallest cog, sitting on very fine splines.