buying guide

Micro Spline vs HG Freehub: Which Shimano 12-Speed Cassette Fits Your Bike?

Buying a 12-speed Shimano cassette is easy — if you know which freehub body is on your rear wheel. Get it wrong and the cassette simply won't slide on. Here's how to tell the difference in 30 seconds, and which cassettes fit what.

The 30-second check

Pull the rear wheel and look at the splined body the cassette slides onto:

  • Micro Spline — 23 small, shallow splines. Introduced by Shimano for 12-speed MTB drivetrains, because only Micro Spline accepts a 10-tooth smallest cog.
  • HG (Hyperglide) — 9 tall splines, one narrower than the rest. The standard that's been on most road and mountain wheels since the 1990s. Smallest cog: 11 teeth.

No tools, no guesswork — the two look completely different once you know what you're looking for.

Mountain bike: which cassette for each freehub

If you have Micro Spline, you can run Shimano's wide-range 12-speed MTB cassettes:

  • Deore XT CS-M8100 10-51T — the do-everything favorite, 510% range, HYPERGLIDE+ shifting under load
  • Deore XT CS-M8100 10-45T — tighter jumps for fitter riders and e-MTBs
  • SLX CS-M7100 10-51T / 10-45T — same gearing at a friendlier price, slightly heavier

If you have HG, a 10-tooth cog physically can't fit — but you still have great 11-speed and wide-range options like the SLX CS-M7000 11-46T, or you can upgrade the freehub body on many hubs (check with your wheel or hub maker — DT Swiss, Industry Nine and most major brands sell Micro Spline conversion kits).

Road & gravel: it's (almost) all HG

Good news: Shimano's 12-speed road cassettes still use the HG road freehub. If you're upgrading to Ultegra or 105 Di2 12-speed:

  • Dura-Ace CS-R9200 (11-30T / 11-34T) — titanium large cogs, superlight
  • Ultegra CS-R8101 / CS-R8100 (11-30T / 11-34T) — the performance sweet spot
  • 105 CS-R7101 11-34T — fits both 11- and 12-speed HG freehubs

All of these fit a standard 11-speed HG road freehub — no wheel changes needed. Browse them all in our cassette collection.

Quick reference

  • Smallest cog is 10T → you need Micro Spline
  • Smallest cog is 11T → you need HG
  • 12-speed MTB (XT/SLX/XTR “M” series) → Micro Spline
  • 12-speed road (Dura-Ace/Ultegra/105 “R” series) → HG road

Still not sure?

Email us at support@brinvo.com with your wheel or hub model and the drivetrain you're running (for example, “DT Swiss M1900, Deore XT 12-speed”) and we'll confirm the right cassette before you buy. Every cassette we sell is 100% genuine Shimano, brand new in retail packaging, with free shipping to the lower 48 and free 30-day returns.
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