Bicycle Cassette Standards Explained: Speeds, Freehub Bodies & Compatibility | BikeQuiver Cyclopedia

The cassette is the stack of sprockets (toothed cogs) on your rear wheel that the chain climbs up and down as you shift. Cassettes come in different speed counts (7 to 13), tooth ranges (like 11-34 or 10-52), and mounting interfaces called freehub body standards. Knowing all three tells you which chains, wheels, and derailleurs will work with your bike.

Why these standards exist

A cassette has to physically lock onto the freehub body — the splined, ratcheting cylinder on your rear hub that lets you coast. For decades nearly everything used Shimano's Hyperglide (HG) spline pattern, so an 8-speed SRAM cassette slid onto the same body as a 10-speed Shimano one. That changed when the industry wanted sprockets smaller than 11 teeth: a 10- or 9-tooth cog is physically smaller in diameter than the old HG body itself, so it simply cannot fit over it. SRAM answered with the XD driver, Shimano with Micro Spline, and Campagnolo with N3W — three new, mutually incompatible interfaces that exist for the same reason.

Speed count matters just as much as the mount. Every time manufacturers added a sprocket, they squeezed the stack into roughly the same overall width by making each sprocket and each spacer thinner. That is why an 11-speed chain is narrower than an 8-speed chain, and why your shifter, cassette, derailleur, and chain generally all need to agree on the number of speeds — the shifter pulls a precise amount of cable (or sends a signal) for each click, matched to the exact sprocket-to-sprocket spacing of the cassette.

Finally, the tooth range (smallest and largest cog) determines how easy your lowest gear is and how fast your highest gear is — and it constrains the rear derailleur, which is only rated up to a certain largest-cog size. Entering your cassette's speed count, cog range, and freehub standard lets BikeQuiver check all of these interactions for you.

Modern standards

What you’ll find on bikes from roughly 2018 onward. Modern bikes run 10-13 speeds on one of four current freehub interfaces: Shimano HG, Micro Spline, SRAM XD/XDR, or Campagnolo N3W. Thread-on freewheels are a vintage/budget signature.

Shimano HG freehub (MTB / 8-10 speed length)

Late 1980s-present

Also called: Hyperglide, HG spline, Shimano splined

Splined body about 34.9 mm long, 9 splines with one wide spline for orientation; threaded lockring holds the cassette

Shimano's Hyperglide freehub moved the ratchet into the hub and let sprockets slide onto splines, held by a lockring. This original body length carries Shimano and SRAM 8-, 9-, and 10-speed cassettes interchangeably, plus Shimano 11- and 12-speed mountain cassettes whose oversized largest cogs overhang inboard of the body. It is the de facto industry standard most other brands copied.

Why it exists: Shimano introduced the freehub to fix the freewheel's weaknesses: bearings could sit out near the frame dropout (stronger axles) and worn sprockets could be replaced without replacing the ratchet mechanism.

Typically found on: The vast majority of mountain, hybrid, commuter, and e-bikes from the 1990s to today with 8-12 speeds and an 11T+ smallest cog

Shimano HG Road 11-speed

2013-present

Also called: HG-EV, HG spline L, road-width HG

Same 9-spline HG pattern but about 36.75 mm long — 1.85 mm longer than the MTB-length body

When Shimano's road groups went to 11-speed (2012-2013), the cassette stack got wider than the classic HG body, so road wheels adopted a body stretched by 1.85 mm. Road 11-speed cassettes need this longer body; narrower 8/9/10-speed cassettes fit it with a 1.85 mm spacer behind them. Shimano's 12-speed road cassettes (with 11T smallest cog) also mount on this body.

Why it exists: Eleven road sprockets at reliable-shifting spacing simply would not fit on the old body length, and road hubs had room to grow the body outboard.

Typically found on: Road and gravel bikes with Shimano 105/Ultegra/Dura-Ace 11- and 12-speed, and SRAM 11-speed road groups

Shimano Micro Spline

2019-present

Also called: MS, Micro Spline 12s

23 small splines on a body about 26 mm long; supports a 10-tooth smallest cog

Shimano's answer to wide-range 12-speed mountain gearing. The many fine splines and shorter body let the smallest 10T cog sit outboard, beyond the end of the body. Used by Shimano 12-speed MTB groups (Deore through XTR) and some gravel/e-bike drivetrains; licensed to major hub brands.

Why it exists: A 10-tooth cog is smaller in diameter than the classic HG body, so Shimano needed a new, slimmer interface to offer 10-51T ranges competing with SRAM Eagle.

Typically found on: Shimano 12-speed mountain bikes (Deore M6100, SLX, XT, XTR) and many mid-to-high-end e-MTBs

SRAM XD

2012-present

Also called: XD driver, XD driver body

Short splined-and-threaded driver; cassette is a one-piece cluster that threads/clamps onto it, allowing a 10-tooth smallest cog

SRAM's driver for wide-range mountain cassettes. Instead of sliding loose sprockets onto splines, the entire machined cassette engages a small spline set and threads onto the driver as one unit. Required for SRAM 11-speed 10-42 and 12-speed Eagle 10-50/10-52 cassettes.

Why it exists: Created for SRAM's 1x11 revolution (XX1, 2012): dropping the front derailleur demanded a 10T small cog for top-end speed, which could not fit over an HG body.

Typically found on: Mid-to-high-end SRAM-equipped mountain and e-mountain bikes (GX, X01, XX1, Eagle Transmission uses the related XD interface)

SRAM XDR

2019-present

Also called: XD Road

Identical spline/thread design to XD but 1.85 mm longer

The road-length version of XD, sized for road hub spacing. XDR bodies take SRAM's 12- and 13-speed road/gravel cassettes (10T or 9T smallest cogs on RED/Force/Rival AXS). An XD mountain cassette fits an XDR body with a 1.85 mm spacer behind it, but an XDR cassette cannot fit a shorter XD body.

Why it exists: SRAM's AXS road groups use a 10-tooth small cog, and road wheels needed a driver matching the 1.85 mm-longer road body convention without re-dishing the wheel.

Typically found on: Road and gravel bikes with SRAM RED, Force, Rival, and Apex eTap AXS 12-speed

Campagnolo freehub (classic)

1990s-present

Also called: Campy freehub, Campagnolo 9-12s body

Campagnolo-specific deep-spline pattern, not interchangeable with Shimano HG; 11T minimum cog

Campagnolo has always used its own spline pattern and its own lockring. One body length covers Campagnolo 9-, 10-, 11-, and 12-speed road cassettes (with appropriate spacers on older, lower counts). Shimano/SRAM HG cassettes do not fit it and vice versa.

Why it exists: Campagnolo developed its freehub independently and kept its own sprocket spacing and spline geometry as a closed ecosystem for its groupsets.

Typically found on: Road bikes equipped with Campagnolo Veloce, Centaur, Athena, Chorus, Record, Super Record

Campagnolo N3W

2020-present

Also called: N3W driver, Ekar freehub

Same 8-ish deep-spline profile as the classic Campagnolo body but noticeably shorter, making room for 9- and 10-tooth cogs

Introduced with the 13-speed Ekar gravel group in 2020. N3W keeps the classic Campagnolo spline shape but shortens the body so the tiny 9T and 10T end cogs can hang outboard. With Campagnolo's adapter, a classic 10/11/12-speed Campy cassette can still be mounted, making N3W backward compatible within the brand.

Why it exists: Ekar's 13-speed 9-36/10-44 ranges start on a 9-tooth cog — far too small for any full-length body — so Campagnolo shortened its own standard rather than adopting XD or Micro Spline.

Typically found on: Gravel bikes with Campagnolo Ekar and Ekar GT; newer Campagnolo/Fulcrum wheels ship N3W

Legacy standards

BikeQuiver focuses on modern bikes, but these earlier standards are worth knowing when you’re identifying parts on an older bike — or figuring out whether a used part will fit a new one.

Show 1 legacy standard

Thread-on freewheel

1900s-1990s on mainstream bikes; still made today

Also called: Screw-on freewheel, Multiple freewheel, Block

ISO threading 1.37 in x 24 TPI on the hub shell; typically 5-7 speeds (some 8)

Before cassettes, the sprockets and the coasting ratchet came as one unit — the freewheel — that screwed onto a large thread on the hub. The whole cluster spins off (with the correct splined remover) and pedaling torque keeps it tight. It is not a cassette and does not use a freehub body.

Why it exists: It was the original derailleur-bike standard: a simple threaded interface any brand could make. It faded because the hub bearings sit inboard of the sprockets, letting axles bend or snap, and because replacing worn sprockets meant replacing the ratchet too.

Typically found on: Vintage road and mountain bikes through the late 1980s, budget bikes, kids' bikes, and many hub-motor e-bike conversions

What to record about yours

These are the values worth writing down when you add this part to your quiver — the critical ones drive compatibility matching.

Spec	Matters for fit	Common values
Speeds (number of sprockets)(speeds) critical	The speed count sets the sprocket spacing and chain width, so the chain, shifter, and rear derailleur must all match it. It is the single most important cassette spec.	12 · 11 · 10 · 9 · 8 · 7 · 13
Cog range (smallest-largest teeth) critical	Written as smallest-largest tooth count (e.g. 11-34, 10-52). It defines your gearing and must stay within your rear derailleur's rated maximum cog and total capacity.	11-34 · 10-52 · 11-28 · 11-32 · 10-51 · 11-30 · 10-50 · 11-36 · 10-33 · 11-42 · 10-45 · 11-25 · 9-13 speed variants of 11-40 · 14-28 (freewheel)
Freehub body standard critical	The spline interface the cassette mounts on. A cassette made for one standard will not fit another, so this determines which wheels/hubs accept your cassette.	Shimano HG (8/9/10/11-speed MTB) · Shimano HG Road 11-speed · Shimano Micro Spline · SRAM XD · SRAM XDR · Campagnolo · Campagnolo N3W · Thread-on freewheel (not a cassette)
Brand helpful	Shimano, SRAM, and Campagnolo each have their own shifting-spacing conventions, so brand plus speed count is the fastest way to predict what else the cassette works with.	Shimano · SRAM · Campagnolo · SunRace · Microshift · KMC/other HG-compatible
Smallest cog (teeth) helpful	A 10-tooth (or 9-tooth) smallest cog is the giveaway that the cassette needs a modern driver — SRAM XD/XDR, Shimano Micro Spline, or Campagnolo N3W — because those cogs are too small to fit over a classic HG body.	11 · 10 · 12 · 13 · 14 · 9
Largest cog (teeth) helpful	The largest cog must not exceed the rear derailleur's rated maximum, and big jumps (e.g. to 50-52T) usually require a long-cage or dedicated wide-range derailleur.	34 · 28 · 32 · 52 · 51 · 50 · 36 · 30 · 42 · 46 · 25
Model / part number optional	The etched model code (e.g. CS-M8100-12, XG-1275, CS-HG500-10) pins down the exact cassette, including its freehub standard and intended drivetrain family.	CS-M8100-12 · CS-HG700-11 · XG-1275 Eagle · PG-1130 · CS-R7000 · CS-LG400-11 (LinkGlide)

How to identify which one you have

Cassette or freewheel? The spin test

Take the rear wheel off and look at the center of the sprocket cluster for a tool fitting (a ring with notches or splines). Spin the sprockets backward: if that fitting spins with the sprockets, you have a thread-on freewheel; if it stays still while the sprockets turn, you have a cassette on a freehub. Freewheels are usually 5-7 speed; cassettes are 7-13 speed.

By the smallest cog

Count the teeth on the smallest sprocket. 11 teeth or more almost always means a Shimano/SRAM HG body or a classic Campagnolo body. A 10-tooth cog means SRAM XD/XDR or Shimano Micro Spline; a 9-tooth cog means SRAM XDR (13s) or Campagnolo N3W. Also look at how the cassette ends: HG cassettes have a visible splined lockring; XD/XDR cassettes look like one sealed machined piece with no separate lockring face.

By counting & measuring

Count the sprockets to get your speed count (stand the wheel up and count the gaps carefully — 11 and 12 are easy to confuse). Read or count teeth on the smallest and largest cogs to get the range (e.g. 11-34). If the cassette is off the wheel, identify the freehub: 9 broad splines with one extra-wide one is Shimano HG (about 34.9 mm long for MTB/8-10s, about 36.75 mm for road 11s); around two dozen fine splines is Micro Spline; a stepped, partly threaded driver is XD/XDR; deep wavy splines are Campagnolo.

By markings

Most cassettes are stamped or laser-etched on the largest sprocket or its carrier: tooth counts per cog, the range (e.g. 10-52T), and a model code. Shimano codes start with CS- (CS-M8100-12 = XT 12-speed, Micro Spline; CS-HG500-10 = 10-speed HG). SRAM uses PG- (pinned, HG-compatible) or XG- (machined, XD/XDR) plus a number whose middle digits hint at tier and speeds (XG-1275 = 12-speed). Campagnolo marks the group name (Chorus, Record, Ekar). Search the code online to confirm speeds and freehub type.

Compatibility gotchas

Match speeds first: the shifter, rear derailleur, chain, and cassette generally must all be the same speed count and (above 10-speed) usually the same brand, because each brand's cable pull and sprocket spacing differ.
Shimano and SRAM 8-, 9-, and 10-speed cassettes are interchangeable with each other and all fit the same standard HG freehub body; a 7-speed cassette fits that body with a 4.5 mm spacer.
Shimano and SRAM 11-speed ROAD cassettes use the same spacing and interchange freely, but they need the longer road HG body (1.85 mm longer). An 8/9/10-speed cassette fits a road 11s body by adding a 1.85 mm spacer behind it.
Shimano 11- and 12-speed MOUNTAIN HG cassettes (11-40T and larger) fit the standard short HG body because the biggest cogs dish inboard past the body — so an 11-speed MTB cassette fits wheels an 11-speed road cassette will not.
A 10-tooth or 9-tooth smallest cog always means a dedicated driver: SRAM XD (MTB), XDR (road, 1.85 mm longer), Shimano Micro Spline, or Campagnolo N3W. None of these interchange with each other or with HG, but most modern hubs let you swap the freehub body itself in minutes.
An XD cassette works on an XDR body with a 1.85 mm spacer; an XDR cassette does not fit an XD body. Similarly, Shimano road 12-speed (11T) cassettes fit the road 11-speed HG body — no new wheel needed.
Campagnolo cassettes only fit Campagnolo-spline bodies (classic or, via adapter, N3W); they never fit HG, XD, or Micro Spline bodies, and Shimano/SRAM cassettes never fit Campagnolo bodies.
Your rear derailleur has a rated maximum largest cog (e.g. 34T for many road units, 51-52T for 12-speed MTB) and a total capacity: (largest cog - smallest cog) + (largest chainring - smallest chainring). A wider cassette than the derailleur is rated for usually needs a longer cage or a different derailleur.
SRAM and Shimano 12-speed MTB cassettes use very similar sprocket spacing, so mixed setups can work in a pinch, but each brand's shifting ramps are tuned for its own chain — expect the best shifting when cassette, chain, and derailleur come from the same system (Shimano LinkGlide cassettes, used on many e-bikes, require LinkGlide-specific chains/derailleurs).
You cannot put a cassette on a freewheel hub or a freewheel on a freehub — they are different hub designs. If your bike (or hub-motor e-bike) has a screw-on freewheel, replace like with like or replace the hub/wheel.

References

Related components

Chain Rear Derailleur Shifters Wheels