Microspline
Microspline is Shimano's freehub for modern 12-speed mountain and gravel drivetrains. It has 23 fine splines (versus HG's 9) and allows a 10-tooth minimum cog, for wide ranges like 10-51T. It's required for Shimano 12-speed MTB cassettes (Deore, SLX, XT, XTR) and GRX 12-speed gravel. It's not compatible with HG or with SRAM's XD.
If you have a Shimano 12-speed mountain bike, your wheel runs Microspline. It's the only way to mount those 10-tooth cassettes.
What it is and why it exists
It works like HG but with 23 smaller splines and a step that leaves the 10T cog overhanging the body. That spline density spreads the load and stops steel cogs from biting into the aluminum freehub. It's Shimano's answer to the modern wide-range 1x.
Key data
What it fits
Only Shimano 12-speed MTB cassettes (Deore M6100, SLX M7100, XT M8100, XTR M9100) and GRX 12-speed gravel. No HG, no SRAM XD/XDR. Brands like DT Swiss, Hope or Mavic sell the Microspline body separately for their modular hubs.
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Frequently asked questions
Does Microspline accept SRAM cassettes?
No. Microspline is exclusive to Shimano 12sp MTB/gravel. A SRAM Eagle cassette uses an XD freehub, an incompatible geometry.
Can I convert my wheel to Microspline?
Depends on the hub. DT Swiss, Hope, Mavic and others sell the Microspline body separately for their modular hubs. On sealed generic hubs, no.
Why 23 splines instead of 9?
They spread the load better over the usually-aluminum body, reducing the «bite» steel cogs make on HG freehubs.