Crankset Standards Explained: Spindle Interfaces, BCD, Crank Length & Chainline | BikeQuiver Cyclopedia

The crankset is the set of crank arms, spindle, and chainrings that turns your pedaling into forward motion. Cranksets attach to the frame through the bottom bracket, and the shape and diameter of the spindle interface decides which bottom bracket fits. Chainring mounting pattern, crank arm length, and chainline decide which chainrings, chains, and frames a crankset works with.

Why these standards exist

The crankset sits at the junction of four other systems: the bottom bracket bearings it spins in, the frame shell those bearings press or thread into, the chainrings bolted to it, and the chain and cassette behind it. Each connection is governed by a named standard, and a mismatch at any one of them means the parts simply will not go together. Knowing your crankset's spindle interface and chainring mounting pattern answers most compatibility questions before you buy anything.

Crank standards accumulated in layers rather than replacing each other. Square taper cranks from the 1970s-90s are still everywhere on commuters and older bikes; splined Octalink and ISIS interfaces ruled the early 2000s; and since about 2004 most new bikes use large hollow spindles permanently pressed into one crank arm (Shimano Hollowtech II, SRAM GXP and DUB, and various 30 mm designs). Because all of these are still in service, identifying which generation you own is the first step in finding replacement parts.

More recent splits add another layer: mountain bikes moved from 3x and 2x chainrings to single-ring (1x) drivetrains, Boost frames pushed the chainline outboard, and direct-mount chainrings replaced bolt circles on many cranks. Each shift created parts that look interchangeable but are not, which is why precise labels matter.

Modern standards

What you’ll find on bikes from roughly 2018 onward. From 2018 on, expect Shimano Hollowtech II, SRAM DUB, or a 30 mm-spindle crank, usually 1x with a direct-mount chainring and (on MTB) Boost chainline. Square taper and Octalink point to an older or entry-level bike.

ISIS Drive

1999-2006 on bicycles; ongoing on e-bike mid-drive motors

Also called: International Splined Interface Standard

22mm diameter spindle with 10 splines, open published dimensions.

An open splined standard created by Race Face, Truvativ, and Chris King as a license-free answer to Shimano's Octalink. Common on early-2000s mountain and BMX cranks. Its bearings were smaller than square-taper ones for the same shell, so ISIS bottom brackets had a reputation for short life. The interface lives on in e-bikes: many mid-drive motors (including most Bosch systems) use an ISIS-splined motor axle, so e-bike crank arms are often ISIS-fit arms bolted to the motor rather than a full crankset.

Why it exists: Component makers wanted a splined spindle like Octalink without paying Shimano to license it, so they published an open standard.

Typically found on: Early-2000s MTB (Race Face, Truvativ), BMX, and current mid-drive e-bikes (Bosch and others use ISIS or proprietary splines)

Shimano Hollowtech II

2003-present

Also called: HTII, 24mm external bearing

Hollow steel spindle, constant 24mm diameter, permanently attached to the right crank arm; left arm clamps on with two pinch bolts over a splined end. Bearings are 24x37x7mm.

The dominant modern crank design. Shimano moved the bearings outboard of the frame shell and made the spindle part of the drive-side crank, which let both spindle and bearings grow larger without frame changes. Most other brands' '24mm' cranks (Race Face EXI, FSA MegaExo, Praxis M24, Rotor 3D24) follow the same bearing fit, so they generally share bottom brackets with Hollowtech II.

Why it exists: Outboard bearings allowed a stiff oversized hollow spindle and bigger bearings while still fitting the classic 68/73mm threaded frame shell.

Typically found on: The majority of Shimano-equipped road, gravel, and mountain bikes from ~2004 onward, every price level from Deore/Tiagra up

SRAM GXP

2004-present (largely replaced by DUB on new SRAM cranks since 2018)

Also called: Giga X Pipe, Truvativ GXP

Stepped steel spindle: 24mm diameter on the drive side, 22mm at the non-drive end. Bearings: 24x37x7mm drive side, 22x37x8mm non-drive side.

SRAM/Truvativ's answer to Hollowtech II. It looks nearly identical, but the spindle steps down to 22mm on the left side, where a shoulder against the non-drive bearing sets the bearing preload. A GXP crank needs a GXP-specific bottom bracket (or a 24mm BB with a GXP adapter); a plain 24mm Shimano bottom bracket will not locate it correctly.

Why it exists: The stepped design self-adjusts bearing preload without the preload cap or careful adjustment that plain 24mm systems need.

Typically found on: SRAM/Truvativ road and MTB cranks ~2005-2018 (Rival, Force, Red, X7/X9/X0, early Eagle)

SRAM DUB

2018-present

Also called: Durable Unified Bottom bracket

Constant 28.99mm (~29mm) aluminum spindle. DUB bottom brackets use 29mm-bore bearings and are made for every common shell: BSA threaded, T47, BB30, PF30, BB86/92.

SRAM's current one-spindle-for-everything standard, launched in 2018 on Eagle MTB cranks and now used across its road, gravel, and MTB lines. The odd 28.99mm size splits the difference between 24mm steel and 30mm aluminum spindles, leaving room for durable seals in every shell type while keeping an aluminum spindle's weight.

Why it exists: SRAM wanted one crank spindle that could fit every frame shell standard with a single bottom bracket family, ending the 24mm-vs-30mm juggling act.

Typically found on: Nearly all current SRAM cranks: Eagle MTB (SX through XX SL), road/gravel Apex through Red AXS

BB30 / 30mm spindle

2006-present

Also called: BB30, PF30, 386EVO, BB386EVO

Straight 30mm aluminum spindle. BB30 cranks have short spindles for 68/73mm-wide BB30 shells; 386EVO cranks use a longer 30mm spindle that spans 86.5mm press-fit shells and adapts to almost any frame.

A family of cranks built around a light 30mm aluminum spindle, originating with Cannondale's BB30 frame standard (2000, opened to the industry ~2006). Short-spindle BB30 cranks only fit BB30/PF30-type frames, while long-spindle 30mm cranks (386EVO, Race Face Cinch, Rotor, Praxis M30 variants) fit most frames using the right bottom bracket. 30mm cranks in narrow threaded BSA shells leave little room for bearings, which is part of why T47 and DUB emerged.

Why it exists: Aluminum is weaker than steel, so an aluminum spindle needs a fatter diameter; 30mm delivered the lightest spindle for a given stiffness.

Typically found on: Cannondale (Hollowgram), FSA, Rotor, Praxis, Easton cranks; common on carbon road and gravel bikes with press-fit shells

Race Face Cinch

2014-present

Also called: Cinch 30mm, Cinch spindle system

30mm aluminum spindle (some gravel/road versions 24mm or 28.99mm), swappable spindles for different shell widths, and a splined Cinch direct-mount chainring interface with a lockring.

Race Face's modular crank platform: the same arms accept different spindle lengths (standard, Boost, Super Boost, fat bike) and Cinch direct-mount chainrings or spider adapters. Widely used on mountain and gravel bikes, and the Cinch ring interface is supported by many aftermarket chainring makers (Wolf Tooth, absoluteBLACK, and others).

Why it exists: One crankset that adapts to many frame widths and ring setups simplifies inventory for riders and shops, and direct-mount rings save weight over a spider.

Typically found on: Race Face Next/Turbine/Aeffect and Easton cranks on modern mountain, fat, and gravel bikes

Bolt-circle (BCD) chainring mounting

1950s-present

Also called: BCD, bolt circle diameter, spider mount

Common patterns: 110mm 5-bolt and 110mm 4-bolt (road compact), 130mm 5-bolt (older road standard), 104mm 4-bolt (MTB outer/middle), 94mm 4-bolt (SRAM MTB), 64mm 4-bolt (MTB inner/granny), 107mm 4-bolt (SRAM road AXS spider).

BCD is the diameter of the imaginary circle passing through the centers of the chainring bolts. A replacement ring must match both the BCD and the bolt count, and modern 4-bolt patterns are often asymmetric (Shimano's 4-bolt 110 road pattern has unevenly spaced holes), so bolt spacing pattern matters too. On a 4-bolt ring the BCD is simply the distance between two opposite bolt holes; on a 5-bolt ring you measure two adjacent holes and convert (5-bolt 110 BCD = 64.7mm between adjacent bolts).

Why it exists: Bolt circles let riders replace worn or differently sized chainrings without buying a whole crankset, and each gearing niche (road double, MTB triple, 1x) evolved its own circle size.

Typically found on: Almost every crank with a spider: 110/130 5-bolt on road cranks pre-2013 and current budget road; asymmetric 110 4-bolt on Shimano road since 2013; 104/64 on MTB triples and many 1x rings

Direct mount chainrings

2013-present

Also called: SRAM 3-bolt DM, Shimano direct mount (8-bolt), Cinch DM

SRAM: 3-bolt spline, in 0mm, 3mm, or 6mm offsets. Shimano MTB (XT/XTR 12-speed) and road Dura-Ace/Ultegra power-meter era: proprietary spline; current Shimano MTB rings attach by a 4-bolt direct pattern behind the arm. Race Face Cinch: splined lockring interface.

Instead of a spider and bolt circle, the chainring splines directly onto the crank arm or spindle, saving weight and allowing smaller rings than any BCD permits. The catch: every brand's spline is proprietary, so a direct-mount ring must be made specifically for your crank brand (and sometimes model). The ring's offset (how far the teeth sit inboard of the mount) is what sets chainline on 1x cranks: 6mm offset for non-Boost, 3mm for Boost, 0mm for Super Boost.

Why it exists: 1x drivetrains eliminated front shifting, so the spider became dead weight; direct mount also lets riders fit tiny rings (down to 26T) impossible on a 104mm BCD.

Typically found on: Most current 1x mountain and gravel cranks: SRAM Eagle and AXS road/gravel, Race Face Cinch, current Shimano XT/XTR

Boost / Super Boost chainline

Boost 2015-present; Super Boost 2017-present

Also called: Boost 148 chainline, 52mm chainline, Super Boost Plus

Non-Boost MTB chainline: 49mm. Boost (148mm rear hub): 52mm. Super Boost (157mm rear hub): 55-56.5mm. Road 2x: about 43.5mm; road/gravel 1x: 45-47.5mm.

Chainline is the distance from the frame centerline to the middle of the chainring (or midpoint between rings on a 2x). When mountain bikes adopted wider Boost 148mm rear hubs around 2015, the cassette moved outboard 3mm, so cranks and rings had to follow. A 'Boost crank' is usually a normal crank with a 3mm-further-out ring position, achieved via ring offset or a longer spindle. Matching crank chainline to the frame's rear-end spacing keeps shifting quiet and the chain from rubbing or falling off.

Why it exists: Wider rear hubs made stronger wheels and cleared bigger tires; each hub-width jump dragged the chainline outboard with it.

Typically found on: Boost: nearly all 2016+ mountain bikes. Super Boost: some enduro bikes (Pivot, Knolly) and many e-MTBs

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 3 legacy standards

Square Taper JIS

1970s-present (dominant until ~2003, still current on budget bikes)

Also called: JIS square taper, cotterless square taper

Square spindle end with a 2-degree taper per side; JIS end is about 12.63mm across. Crank pulls on with an 8mm hex or 14mm square-drive bolt.

The classic crank interface: each crank arm has a square tapered hole that wedges onto a matching square spindle end. JIS (Japanese Industrial Standard) is the far more common of the two square taper variants, used by Shimano and nearly every Asian manufacturer. It is simple, cheap, and durable, which is why it still ships on new commuter and entry-level bikes today.

Why it exists: Cotterless square tapers replaced hammered-in cotter pins in the 1970s, making crank removal a simple puller-tool job and allowing lighter aluminum cranks.

Typically found on: Commuters, entry-level and vintage road/mountain bikes, most bikes made before the mid-2000s

Square Taper ISO

1970s-present (rare on new bikes outside Campagnolo-equipped builds)

Also called: ISO square taper, Campagnolo taper

Same 2-degree taper as JIS but a longer taper ending in a smaller ~12.5mm tip, so the crank sits differently on the spindle.

The European flavor of square taper, used by Campagnolo, Stronglight, TA, and other European makers. An ISO crank on a JIS spindle sits about 4.5mm farther outboard than intended; the combination often works in practice but changes chainline and is not officially compatible.

Why it exists: European manufacturers standardized their existing taper dimensions through ISO while Japanese makers standardized theirs through JIS, leaving two subtly incompatible squares.

Typically found on: Vintage and modern Campagnolo road cranks, older French and Italian bikes

Shimano Octalink

1997-2004 (superseded by Hollowtech II)

Also called: Octalink V1, Octalink V2

22mm diameter spindle with 8 splines. V1 (road: Dura-Ace 7700, Ultegra 6500) uses 5mm-deep splines; V2 (MTB and later road) uses 9mm-deep splines. V1 and V2 cranks are not interchangeable.

Shimano's proprietary splined interface that replaced square taper on its mid- and high-end groups in the late 1990s. The larger hollow spindle was stiffer and lighter than square taper, but the two incompatible versions and the proprietary license limited its spread.

Why it exists: Square taper spindles had to be thin to leave crank material around the hole; splines allowed a fatter, stiffer, hollow spindle without that penalty.

Typically found on: Late-90s/early-2000s Shimano-equipped road and mountain bikes (Dura-Ace 7700, XT M750-era, LX, 105)

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
Spindle interface critical	The spindle (axle) shape and diameter determines which bottom bracket the crankset fits. This is the single most important crankset spec for compatibility.	Shimano Hollowtech II (24mm) · SRAM DUB (28.99mm) · SRAM GXP (24/22mm) · Square Taper JIS · 30mm (BB30/386EVO) · Race Face Cinch (30mm) · ISIS Drive · Octalink V2 · Octalink V1 · Square Taper ISO
Crank arm length(mm) critical	Measured center of the spindle hole to center of the pedal hole; it affects knee bend, cadence, and pedal-to-ground clearance. The length is usually stamped on the back of the arm.	170 · 175 · 172.5 · 165 · 160 · 155 · 150
Chainring mounting critical	How chainrings attach to the crank — either a bolt circle (BCD) or a brand-specific direct mount spline — determines which replacement rings fit.	110mm BCD 4-bolt · SRAM 3-bolt direct mount · Shimano direct mount (8-bolt) · Race Face Cinch direct mount · 104mm BCD 4-bolt · 110mm BCD 5-bolt · 130mm BCD 5-bolt · 94mm BCD 4-bolt · 64mm BCD 4-bolt (inner ring)
Chainring teeth helpful	Tooth count sets your gearing; on 1x drivetrains a single number (e.g. 32T), on 2x/3x listed largest first (e.g. 50/34T). It must suit your chain's speed count and your derailleur's capacity.	32 · 30 · 34 · 50/34 · 52/36 · 46/33 · 40 · 48/31 · 42 · 44/32/22
Number of chainrings helpful	1x (single ring) drivetrains use narrow-wide rings and no front derailleur; 2x and 3x cranks need shift-ramped rings and matching front shifting. Cranks are usually designed for one configuration.	1x · 2x · 3x
Chainline(mm) helpful	The distance from the bike's centerline to the middle of the chainring(s). It must roughly match the rear cassette's position: modern Boost mountain bikes want about 52mm, older MTBs 49mm, road bikes about 43.5-45mm.	52 (MTB Boost) · 49 (MTB non-Boost) · 43.5 (road 2x) · 45 (road/gravel 1x) · 55 (Super Boost) · 47.5 (gravel wide)
Q-factor(mm) optional	The outside-to-outside width between the two pedal faces of the crank arms — your stance width. It is a fit preference, not a hard compatibility spec, but wider frames (fat bikes, Boost MTB) force wider Q-factors.	168-176 (MTB) · 146-150 (road) · 160-165 (gravel) · 200+ (fat bike)
Pedal thread optional	Virtually all modern three-piece cranks use 9/16" x 20 tpi pedal threads (left arm reverse-threaded), so any standard pedal fits. Only old one-piece cranks on department-store and BMX bikes use 1/2".	9/16" x 20 tpi · 1/2" x 20 tpi (one-piece cranks)

How to identify which one you have

By looking at the crank and spindle

Look at where the left crank arm meets the frame. Two small pinch bolts on the left arm clamping a splined spindle means a modern two-piece crank (Hollowtech II, GXP, DUB, or 30mm — check the spindle diameter or logo). A single large bolt hidden under a dust cap in the center of the arm means square taper, Octalink, or ISIS: pull the crank (or peek behind it) and count — a square hole is square taper, 8 splines is Octalink, 10 splines is ISIS. Bearings sitting in cups outside the frame shell also indicate a modern external-bearing system.

By measuring

Crank length: measure center of the spindle hole to center of the pedal hole (usually also stamped on the arm's back). Spindle diameter with calipers: 24mm constant = Hollowtech II family; 24mm stepping to 22mm on the left = GXP; ~29mm = SRAM DUB; 30mm = BB30/386EVO/Cinch; 22mm splined = Octalink or ISIS. Chainring BCD: on a 4-bolt ring, measure hole-center to hole-center across the ring; on a 5-bolt ring, measure two adjacent holes and multiply by 1.701 (adjacent spacing of 64.7mm = 110 BCD; 76.4mm = 130 BCD).

By markings

Most of the answer is printed on the parts. Crank arms carry the brand, model (e.g. FC-M8100, SRAM GX Eagle DUB), and length in mm on the backside. Chainrings usually have the BCD and tooth count stamped near a bolt hole (e.g. '32T 104BCD') and direct-mount rings state their offset (0/3/6mm) and brand fit. 'DUB' is printed on SRAM spindle ends; 'Hollowtech II' appears on Shimano arms. Search the model code online to confirm full specs.

By bike model lookup

If the bike is stock, the manufacturer's spec sheet for your model year lists the crankset make, model, arm length, and chainring sizes. Confirm against the stamped markings, since shops and previous owners often swap cranks and rings.

Compatibility gotchas

The spindle interface must match the bottom bracket exactly: a Hollowtech II (24mm) crank needs a 24mm-bore bottom bracket, DUB needs a DUB bottom bracket, and GXP needs a GXP-specific unit — a plain 24mm Shimano-fit BB will not correctly support GXP's 22mm left end.
Almost any modern crank fits almost any frame if you choose the right bottom bracket, because BB makers (Wheels Mfg, Hope, Chris King, SRAM, Shimano) sell every spindle bore for every shell standard. The exceptions: short-spindle BB30 cranks only fit BB30/PF30 frames, and 30mm spindles in narrow BSA-threaded shells require slimmer, shorter-lived bearings.
Square taper JIS and ISO are officially incompatible: an ISO crank on a JIS spindle sits about 4.5mm farther outboard, changing chainline. It is sometimes workable, but match the standard when you can.
Octalink V1 and V2 look identical but have different spline depths and do not interchange; ISIS (10 splines) does not interchange with Octalink (8 splines) despite both being 22mm.
Chainrings must match BCD, bolt count, and bolt spacing pattern — Shimano's modern 4-bolt road pattern is asymmetric, so a symmetric 110 BCD 4-bolt ring will not fit it. Direct-mount rings are brand-proprietary: a SRAM 3-bolt ring will not fit a Race Face Cinch crank.
For 1x drivetrains, match ring offset to frame spacing: 6mm offset (49mm chainline) for non-Boost, 3mm offset (52mm) for Boost, 0mm (55mm+) for Super Boost. A non-Boost crank on a Boost frame gives a crossed chain in low gears and poor chain retention.
Chainrings are speed-specific at the margins: 12-speed chains are narrower, and Shimano's 12-speed road cranks and SRAM AXS road (which uses a unique flat-top chain) need matching rings. 8/9/10-speed rings tolerate more mixing.
Crank length does not affect mechanical compatibility — any length fits — but shorter arms (160-165mm) are increasingly specced for better ground clearance on MTB and open hip angles on road/gravel; going shorter mainly means raising your saddle slightly.
E-bike mid-drives (Bosch, Brose, Shimano EP-series, Yamaha) have the spindle built into the motor, typically with ISIS splines or a proprietary fitting — you replace only the crank arms and chainring, matched to the motor, not a complete crankset.
Pedal threads are effectively universal: all multi-piece cranks take 9/16" x 20 tpi pedals, with the left side reverse-threaded. Only one-piece (Ashtabula) cranks on old cruisers and kids' bikes use 1/2" pedals.

References

Related components

Bottom Bracket Chain Pedals