Whether a cassette fits a wheel comes down to the freehub body, the splined sleeve the cassette slides onto. Whether a wheel fits a bike comes down to two numbers: the hub's width and its axle's diameter. There are seven freehub bodies and more than a dozen axle standards in use, spread across brand pages that each cover only their own parts. Here they are in one place.
Will this cassette fit?
—
For the workshop wall
The compatibility matrix and the axle table print as one page. No email, no signup.
| Cassette | HG | HG 11 road | Micro Spline | XD | XDR | Campy | N3W |
|---|---|---|---|---|---|---|---|
| 7-speed (HG) | S | S | — | — | — | — | — |
| 8-, 9-, 10-speed (Shimano, SRAM) | ● | S | — | — | — | — | — |
| Shimano 11-speed MTB | ● | S | — | — | — | — | — |
| 11-speed road, 11T smallest (Shimano, SRAM) | — | ● | — | — | — | — | — |
| Shimano 12-speed road | — | ● | — | — | — | — | — |
| Shimano CUES / Linkglide | ● | S | — | — | — | — | — |
| Shimano 12-speed MTB (10T) | — | — | ● | — | — | — | — |
| SRAM 10T MTB (Eagle XX/X0/GX, 11-speed 10-42) | — | — | — | ● | S | — | — |
| SRAM NX / SX Eagle (11T smallest) | ● | S | — | — | — | — | — |
| SRAM 12-speed road AXS (10T) | — | — | — | — | ● | — | — |
| Campagnolo 9–12-speed | — | — | — | — | — | ● | S |
| Campagnolo 13-speed (Ekar) | — | — | — | — | — | — | ● |
S = fits with a spacer or adapter: 1.85 mm for 8–10-speed and MTB cassettes on an 11-speed road body or XD cassettes on XDR; 4.5 mm for 7-speed on HG; Campagnolo's AC21-N3W adapter for 9–12-speed on N3W. A freehub body is usually swappable on the same hub — check with the hub maker.
| Front | Spacing × axle | Used on | Rear | Spacing × axle | Used on |
|---|---|---|---|---|---|
| Quick release | 100 × 9 | Rim-brake road, older MTB and hybrids | Road quick release | 130 × 10 | Rim-brake road |
| 12 mm thru-axle | 100 × 12 | Disc road and gravel | MTB / disc quick release | 135 × 10 | Older MTB, disc road, hybrids |
| 15 mm thru-axle | 100 × 15 | Pre-Boost MTB, early disc road | 135 × 12 thru-axle | 135 × 12 | Early thru-axle frames |
| 20 mm thru-axle | 100 × 20 | Older downhill forks | 142 × 12 thru-axle | 142 × 12 | Disc road, gravel, pre-Boost MTB |
| Boost 12 | 110 × 12 | Some gravel bikes and e-bikes | Boost | 148 × 12 | Modern MTB, some gravel and e-bikes |
| Boost | 110 × 15 | Modern MTB | 150 × 12 DH | 150 × 12 | Older downhill |
| Boost 20 | 110 × 20 | Downhill and some enduro forks | Super Boost / 157 DH | 157 × 12 | Some trail and downhill bikes |
| Fat bike | 150 × 15 | Fat bikes | Fat bike | 197 × 12 | Fat bikes (177 and 197 exist) |
Spacing = hub width between the locknuts (mm); axle = its diameter (quick releases: the hollow axle, not the 5 mm skewer). Thru-axle thread pitch varies (1.0, 1.5, 1.75 mm), so axles don't swap between frames.
Which freehub body do I have?
Take the cassette off and look. A Shimano HG body is long and splined, with one spline wider than the others so the cassette only goes on one way. The 11-speed road version looks the same and is 1.85 mm longer. Micro Spline has many fine, shallow splines. SRAM XD and XDR are short, stepped bodies with a thread at the end, because the cassette screws on as a single piece. Campagnolo bodies have narrower splines in a different pattern, and N3W is Campagnolo's shorter 13-speed body. The hub maker's model number, printed on the hub shell, settles any doubt.
Why does a 10-tooth cog need a special freehub?
A cog can't be smaller than the thing it sits on. An HG body's diameter stops the smallest cog at 11 teeth, so 10- and 9-tooth cogs need a body that steps down at the end, with the smallest cogs overhanging it. That's the whole reason SRAM made XD, Shimano made Micro Spline and Campagnolo made N3W. It's also why the chart splits on the smallest cog: SRAM's own 12-speed cassettes go on HG if they start at 11 teeth (NX and SX Eagle) and on XD if they start at 10.
The 11-speed road HG body is 1.85 mm longer than the 8–10-speed one, and SRAM's road XDR driver is 1.85 mm longer than its mountain XD. Two brands, two generations, the same number: road cassettes needed the extra room for a wider spread of cogs. It's why the fix is the same in both directions: a 1.85 mm spacer lets the shorter mountain cassette sit correctly on the longer road body, and why the longer road cassette never fits the shorter body.
Can I put an 11-speed cassette on a 10-speed hub?
Usually not, if it's an 11-speed road cassette: it needs the longer road body, and the 8–10-speed body is 1.85 mm too short. (A few wide-range 11-speed road cassettes were designed to fit it, and their listings say so.) Shimano's 11-speed mountain cassettes go on the standard HG body. Going the other way is easy: 8-, 9- and 10-speed cassettes fit the 11-speed road body with a 1.85 mm spacer behind them. Some 10-speed cassettes want an extra 1.0 mm, so use the spacers the cassette maker lists. Shimano's 12-speed road cassettes fit the 11-speed road body.
Can I change my freehub body instead of buying a wheel?
On most modern hubs, yes. DT Swiss, Hope and most wheel brands make the body a separate, swappable part: pull the end cap, slide the body off, fit the new one. That's how one wheelset runs a road cassette one season and SRAM Eagle the next. Budget hubs with a body that's part of the hub are the exception. Check the hub maker's list for your exact model before ordering.
Bike axle standards: front and rear
A wheel fits a frame by its hub spacing (the width between the outer faces) and its axle diameter. Measure the spacing with calipers across the hub's end caps, and the axle across the thru-axle or the hollow quick-release axle.
Identify an axle standard
Enter the hub spacing.
Boost vs non-Boost: what actually changed
Boost widened mountain bike hubs from 142 to 148 mm at the rear and 100 to 110 at the front. That's 3 mm per side at the rear and 5 at the front, and the hub flanges moved out with it. Wider flanges brace the spokes at a steeper angle, which makes a stiffer wheel; that's why Boost arrived alongside 29-inch mountain bikes. The drivetrain also moved: Boost puts the chainline 3 mm further out, which leaves more room between tire and chainring. That's why Boost cranks and chainrings have their own offsets. A non-Boost wheel won't go in a Boost frame without spacer kits, and those only work when the dish can be corrected, so it's a job for a wheel builder.
Why won't my thru-axle fit another bike?
Same diameter, different axle. Thru-axles differ in length (the frame or fork's width plus the threaded end) and in thread pitch: 1.0, 1.5 or 1.75 mm depending on the frame maker. A 12 × 142 axle from one frame can screw into another by a turn and then jam, or seem to tighten while holding on two threads. Buy replacement axles by the frame or fork maker's part number, never by "12 mm". Thru-axles usually tighten to 10–15 N·m (often printed on the axle); some are lower, such as Shimano's E-Thru at 5–7.5. The torque chart has the rest.