Micro Spline vs HG vs XD: Which Freehub Body Does Your Cassette Actually Need?

Your cassette decides your freehub body. A Shimano 12-speed SLX, XT or XTR cassette needs a Micro Spline body and will not go on a standard HG body. SRAM Eagle cassettes with a 10-tooth cog (GX, X01, XX1) need XD, or XDR with a spacer. SRAM 12-speed road cassettes need XDR, and Campagnolo uses its own bodies (N3W, plus N3W-BT for 13-speed). Classic 7- to 10-speed Shimano and SRAM cassettes all share the HG spline.

This guide is for anyone about to buy a new cassette or a new wheelset and unsure which standard applies. Every rule below comes from L'Atelier's technical guides (la-telier.com). Where two of those guides disagree, we say so and tell you what to check on your own hub.

The six freehub body standards at a glance

There used to be a single freehub standard. Once drivetrains moved to 10, 11, 12 and then 13 speeds, and the brands started competing on gear range, the field split into six main standards that are not interchangeable. Order the wrong cassette for your wheel and the box goes straight back.

According to L'Atelier, the HG body is about 35 mm long and is fitted to roughly 90% of entry-level and mid-range wheels. That is why it is the default assumption, and also why so many upgrade plans go wrong: the moment you move to a 10-tooth smallest cog, you have left HG behind.

Shimano: HG vs HG+ vs Micro Spline

HG is the original HyperGlide standard, in use since the 1990s, with 9 asymmetric splines. Its known weakness: the smallest cogs dig into an aluminum body over time. HG+ has the same dimensions but one wider spline to handle the torque of 11- and 12-speed cassettes. HG+ cassettes are backward compatible with HG bodies, but they bite harder into aluminum, and Shimano recommends a steel body for HG+.

Micro Spline arrived in 2018 with XTR M9100. It uses 23 finer splines on a smaller body, which is what makes a 10-tooth smallest cog possible (HG tops out at an 11-tooth minimum) and opened the door to 10-51 cassettes. It is mandatory for Shimano 12-speed MTB (M7100, M8100, M9100), and L'Atelier's quick table also lists Shimano's 12-speed road groups (105, Ultegra, Dura-Ace, R7100 onward) on Micro Spline.

If your hub is HG and you want Shimano 12-speed, L'Atelier gives two routes:

• Swap the freehub body for a Micro Spline body made for your hub (DT Swiss, Shimano and others offer them), then run a 10-51 cassette.
• Use a 12-speed cassette made for HG, accepting the 11-tooth smallest cog.
• Remember the rest of the upgrade: going from Shimano 11- to 12-speed also means a new cassette, chain, derailleur and shifter. The frame, the narrow-wide chainring, brakes and cables can stay.

SRAM: XD vs XDR (and where HG still fits)

XD is SRAM's body for cassettes with a 10- or 9-tooth smallest cog: XX1, X01 and GX Eagle 12-speed. The smallest cog threads directly onto the body. It is incompatible with HG and Micro Spline. L'Atelier's 1x guide gives the XG-1295 (X01 Eagle) and XG-1299 (XX1 Eagle) as 10-52T cassettes on an XD driver.

XDR (XD Road) is 1.85 mm longer than XD to take SRAM's 12-speed road cassettes (Red, Force, Rival). The direction of compatibility matters:

• An XD (MTB) cassette fits an XDR body with a spacer.
• An XDR road cassette does NOT fit a standard XD body.
• SRAM's entry-level NX and SX Eagle cassettes are listed on the HG body in L'Atelier's quick table, which is why a cheaper Eagle build can run on an ordinary wheel.
• SRAM 11-speed road cassettes (Rival, Force 11s) also sit on HG.

This is the most common mismatch in US mountain biking right now: "12-speed" does not mean "compatible." A SRAM Eagle 12s cassette (XD) and a Shimano XT 12s cassette (Micro Spline) do not fit the same body. The same split shows up on gravel bikes, where wide 1x cassettes (10-44, 10-50, 10-52) borrow mountain bike standards such as Micro Spline and XD/XDR.

The Campagnolo exception

Campagnolo is a closed ecosystem. Its freehub bodies have a unique spline profile, smaller than Shimano HG, and they are incompatible with HG and SRAM XD. A Campagnolo cassette does not fit an HG body, and vice versa.

• N3W: the current body for all Campagnolo 12-speed cassettes (Chorus, Record, Super Record). It also accepts 11-speed Campagnolo cassettes, via an adapter or directly depending on the model.
• N3W-BT: the variant for the 13-speed Super Record Wireless cassette (9-36), whose smallest sprocket drops to 9 teeth. Physically identical to N3W, but with a thinner small sprocket.
• Tooling: the N3W lockring needs Campagnolo's UT-FT001, which is different from Shimano's lockring tool.
• Availability: N3W bodies are offered by most high-end wheel makers (Fulcrum, Mavic, DT Swiss, Zipp).

The spacer trap and other costly mistakes

Most failed cassette installs come down to length, not splines. L'Atelier's compatibility guide lists these traps:

1. The forgotten spacer. Fitting a 10-speed cassette on an 11-speed body without the 1.85 mm spacer means the lockring cannot clamp the cassette properly.
2. An old 8/9/10-speed wheel for an 11-speed cassette. An 11-speed cassette needs a slightly longer HG body. Most modern wheels are fine, older ones may not be. Note: L'Atelier's compatibility guide gives the extra length as 1.85 mm, while its 10-to-11-speed conversion article cites 2.5 mm for road. Measure, or check your hub maker's spec, before buying.
3. Assuming any hub can switch. DT Swiss offers conversion kits (HG, Micro Spline, XD, XDR, Campagnolo), Hope has interchangeable bodies on Pro 4 and Pro 5 hubs, and Mavic uses its ID360 system. But some entry-level hubs have a fixed body: changing standard means changing the whole wheel.
4. Confusing a freewheel with a cassette. A threaded freewheel (1 to 7 speeds) cannot be converted to a cassette: the hub has to be replaced, which usually means a new wheel.
5. Guessing the lockring torque. L'Atelier's torque chart gives 40 Nm for the cassette lockring, the same for Shimano, SRAM and Campagnolo. Always confirm against the value printed on the part.

How to identify your freehub body before you order

1. Check it is a cassette at all. A splined lockring in the center means cassette; a notched nut means freewheel. Spin the cogs backward by hand: on a cassette only the sprockets turn while the freehub clicks inside the hub.
2. Count the smallest cog. 11 teeth or more usually means HG/HG+. A 10-tooth cog means Micro Spline, XD or XDR. A 9-tooth cog points to SRAM XD or Campagnolo N3W-BT.
3. Read the cassette reference, not just the group name (remember the Deore M6100 case).
4. Look up your hub model to see whether a different body is available.
5. Compare all four drivetrain parameters: speed count, derailleur pull ratio, derailleur capacity, freehub body. If one does not match, the drivetrain will not index, will skip, or will not install.