Bottom Bracket Standards Explained: BSA, T47, BB30, PF30, BB86/92 & More | BikeQuiver Cyclopedia

The bottom bracket is the bearing assembly that lets your cranks spin in the frame. It must match two things at once: the frame's bottom bracket shell (width, diameter, threaded or smooth) and the crankset's spindle (the axle passing through it). Because many competing standards exist, identifying yours correctly is the key to buying a replacement that fits.

Why these standards exist

For decades almost every bike used a threaded shell in one of a few sizes, with English (BSA) threading dominating. The bottom bracket was a sealed cartridge or cup-and-cone unit whose spindle ends matched the crank arms — first square tapers, later splines like Shimano Octalink and ISIS. Identification was simple: shell width plus thread type plus spindle length.

In the 2000s, makers chased stiffer, lighter frames and fatter crank spindles. Threaded cups limited spindle diameter to about 24 mm, so Cannondale's BB30 pressed bearings directly into a larger smooth (unthreaded) shell to fit a 30 mm spindle. Competing press-fit variants followed — PF30, Shimano's BB86/BB92, Trek's BB90/BB95, Cervelo's BBright, FSA's BB386EVO — each with its own bore and width, creating today's confusing landscape.

Press-fit shells in carbon frames proved hard to make to tight tolerances, and slightly loose fits caused the infamous creaking that plagued bikes through the 2010s. The industry has since drifted back to threads: T47 (2015, Chris King and Argonaut) puts threads in a large-diameter shell, and many brands — including Trek and Cannondale — have returned to T47 or classic BSA threading on new bikes.

One more wrinkle: the bottom bracket must also match the crank spindle passing through it. The frame's shell standard and the crank's spindle interface (24 mm Hollowtech II, SRAM DUB 28.99 mm, 30 mm, GXP, square taper, etc.) are independent choices, and the bottom bracket is the adapter between them. Most shells accept several spindle types if you buy the right bottom bracket model.

Modern standards

What you’ll find on bikes from roughly 2018 onward. Modern frames are consolidating on threaded BSA and T47 plus the BB86/BB92 press-fit family, driven by 24 mm (Shimano), 28.99 mm (SRAM DUB), and 30 mm spindles. Square taper, Octalink, and ISIS cranks signal an older or budget bike — except ISIS-like interfaces living on inside e-bike mid-drives.

BSA (English/ISO threaded)

Early 1900s-present

Also called: English, BSC, ISO threaded, 68 mm threaded, 73 mm threaded

1.37 in x 24 TPI threads (~34.8 mm); shell width 68 mm (road) or 73 mm (MTB); also 83 mm (DH) and 100 mm (fat bike)

The default threaded standard for over a century and still the most common worldwide. The drive-side cup is reverse (left-hand) threaded so pedaling forces cannot unscrew it. Accepts everything from cartridge square-taper units to modern external-bearing cups for 24 mm, DUB, and 30 mm cranks.

Why it exists: Inherited from British bicycle industry threading. Its reverse-threaded drive cup solved self-loosening, which is why it outlived French and Italian threading.

Typically found on: Most steel, aluminum, and titanium frames of any era; nearly all commuters and budget bikes; most modern mountain bikes; many 2020s road/gravel bikes as brands return to threads

T47

2015-present, mainstream from ~2019

Also called: Thread 47, T47 internal (T47i), T47 external, T47 85.5 (Trek)

M47 x 1.0 mm threads (~46 mm bore); widths 68/73 mm (external-bearing versions) or 85.5/86.5 mm (internal-bearing versions)

The modern threaded standard: essentially a PF30-sized shell with threads cut into it. Created in 2015 by Chris King and Argonaut Cycles, it keeps the large bore that fits 30 mm and DUB spindles while eliminating press-fit creak. Versions exist with bearings outboard or inboard of the shell, so note your shell width.

Why it exists: A direct response to the press-fit creaking era — the industry wanted big spindles and serviceable, quiet threads at the same time.

Typically found on: Trek road/gravel (T47 85.5) since ~2019, many US custom builders, Cannondale, Santa Cruz, Salsa, and a growing list of 2020s road, gravel, and mountain frames

PF30

2009-present, declining

Also called: PressFit 30, OSBB (Specialized carbon, similar)

46 mm smooth bore; shell width 68 mm (road) or 73 mm (MTB); bearings arrive pressed in plastic or alloy cups

BB30's more forgiving sibling: the same 30 mm-spindle-friendly bearings sit inside cups that press into a 46 mm bore. The cups absorb small frame tolerance errors — though creaking still occurred, spawning aftermarket thread-together PF30 units.

Why it exists: SRAM introduced it (2009) so carbon frames would not need the precision-machined bore that BB30 demands.

Typically found on: Many 2010s carbon road and MTB frames from Specialized, Cannondale, Pivot, and others

BB86/BB92

2008-present

Also called: PressFit 41, PF86, PF92, Shimano Press-Fit, BB89.5

41 mm smooth bore; shell width 86.5 mm (road, BB86) or 89.5/92 mm (MTB, BB92); 37 mm OD bearings in press-in cups; native 24 mm spindle

Shimano's press-fit answer: take a threaded external-cup setup (bearings outboard of a 68/73 mm shell) and mold the frame shell out to enclose those bearings. Its 41 mm bore fits 24 mm cranks naturally; DUB cranks work with specific bottom brackets using smaller bearings.

Why it exists: Let frame makers widen the shell for stiffness and drop threaded inserts while keeping Shimano's proven 24 mm spindle and bearing placement.

Typically found on: Huge range of 2010s-2020s carbon road bikes (Giant, Canyon, Pinarello, Scott) and most carbon MTB frames before the recent return to threads

BB90/BB95 (Trek)

2007-~2020, replaced by T47 on newer Treks

Also called: Trek BB90, Trek BB95

37 mm bore; shell width 90.5 mm (road, BB90) or 95.5 mm (MTB, BB95); bare 37 x 24 x 7 mm bearings press directly into the frame

Trek's proprietary system: the carbon shell is molded so standard Shimano-size bearings press straight in with no cups, placed exactly where external cups would sit. Only 24 mm spindle cranks fit — no room for DUB or 30 mm spindles.

Why it exists: Trek wanted the widest, lightest shell for the Madone (2007) without cup hardware.

Typically found on: Trek Madone, Domane, Emonda, Fuel EX and other Treks from ~2007-2020

BBright

2011-~2020

Also called: BBright Press Fit, BBright Direct Fit

Shell width 79 mm, asymmetric (extended 11 mm on the non-drive side); press-fit version 46 mm bore, direct-fit version 42 mm bore; 30 mm or shorter spindles via adapters

Cervelo's asymmetric standard: a BB30/PF30 shell stretched toward the non-drive side to widen the frame tubes there. Cranks need a spindle long enough for the 79 mm shell — BBright-specific or BB386EVO/DUB cranks fit; standard BB30 road cranks do not.

Why it exists: Cervelo argued the non-drive side had free space (no chainrings) that could hold wider, stiffer frame tubes.

Typically found on: Cervelo R and S series road bikes of the 2010s

BB386EVO

2011-present

Also called: 386EVO, BB392EVO (MTB variant)

46 mm smooth bore; shell width 86.5 mm (road) or 92 mm (MTB, BB392EVO); 30 mm spindle with extra length

Combines PF30's 46 mm bore with BB86's wide 86.5 mm shell. Cranks made for it have long 30 mm spindles that also fit nearly every other standard with adapters, which made 386EVO cranks popular as a universal choice.

Why it exists: FSA and BH (2011) wanted PF30's big spindle and BB86's wide shell in one standard.

Typically found on: BH, Wilier, some Bianchi, Look and open-mold carbon road frames; many FSA and Praxis cranks use its spindle format

BB30A / PF30A (Cannondale asymmetric)

2014-~2021

Also called: BB30-83 Ai, PF30-83 Ai (MTB)

Like BB30/PF30 but 73 mm shell on road bikes, extended ~5 mm on the non-drive side (42 mm bore for BB30A, 46 mm for PF30A)

Cannondale's asymmetric update of its own standards: the shell grows only on the non-drive side, so cranks need an 'A' spindle or spacer setup. Visually identical to BB30/PF30 from below — measure the width and check the model year to tell them apart.

Why it exists: Same logic as BBright: use free non-drive-side space for stiffness without changing chainline.

Typically found on: Cannondale Synapse, SuperSix Evo, CAAD12, and F-Si/Scalpel MTBs of the mid-late 2010s

Shimano Hollowtech II (24 mm external bearing)

2003-present

Also called: HTII, 24 mm spindle, External bearing threaded

24 mm hollow steel spindle permanently attached to the drive crank; bearing cups thread into BSA 68/73 mm shells and sit outboard of the shell faces

The dominant crank/BB system since the mid-2000s: moving the bearings outside the shell allowed a big 24 mm spindle in a standard threaded frame. The same 24 mm spindle also runs in BB86/92, BB90/95, and (with adapters) BB30/PF30/T47 frames. FSA MegaExo, Race Face and others copied the outboard layout.

Why it exists: Achieved oversized-spindle stiffness without abandoning threaded shells.

Typically found on: Nearly all Shimano-equipped road, gravel, and mountain bikes since ~2004

SRAM GXP

~2005-present, largely replaced by DUB

Also called: Giga X Pipe

Stepped spindle: 24 mm on the drive side, 22 mm at the non-drive bearing; threaded external cups for BSA shells plus press-fit GXP versions

SRAM/Truvativ's external-bearing system. Looks like Hollowtech II but the non-drive end steps down to 22 mm, so GXP cranks need GXP-specific bottom brackets (or conversion bearings) — a common mismatch trap when replacing a 24 mm bottom bracket.

Why it exists: The stepped 22 mm end lets the non-drive bearing clamp the spindle and self-locate, avoiding preload adjusters.

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

SRAM DUB

2018-present

Also called: Durable Unified Bottom bracket, 28.99 mm spindle

28.99 mm (~29 mm) aluminum spindle; one spindle standard with DUB bottom brackets made for BSA, T47, BB30, PF30, BB86/92, and wide/fat variants

SRAM's 2018 unification: a single 28.99 mm spindle sized between 24 and 30 mm, paired with a bottom bracket for virtually every shell standard. The odd diameter leaves room for better bearing seals than a true 30 mm spindle allows. Nearly all current SRAM cranks use DUB.

Why it exists: Replaced SRAM's split 24 mm GXP / 30 mm BB30 lineup with one spindle that fits everything via the bottom bracket.

Typically found on: SRAM Eagle-equipped mountain bikes and SRAM AXS road/gravel bikes from 2018 on

E-bike mid-drive (motor bottom bracket)

2010-present

Also called: Mid-motor mount, Bosch/Shimano STEPS/Brose motor interface

No standard BB shell — the motor housing bolts into a motor-specific frame cavity; crank arms mount to the motor's own spindle (often a square taper or ISIS-like interface)

On mid-drive e-bikes the motor replaces the bottom bracket entirely: there is no BB shell or BB standard, and 'bottom bracket' replacement means motor service. Only the crank arms are user-replaceable, and they must match the motor's spindle (many Bosch and Brose motors use ISIS or square taper arms). Hub-motor e-bikes keep a normal BB, and Bafang-style retrofit motors clamp into 68-73 mm BSA shells.

Why it exists: Placing the motor at the crank gives natural pedal-assist feel, but requires a proprietary frame interface.

Typically found on: Bosch, Shimano STEPS, Brose, Yamaha, Specialized, and Fazua equipped e-bikes

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 5 legacy standards

Italian threaded

1940s-2010s, now rare on new bikes

Also called: ITA, 36 x 24

36 mm x 24 TPI threads; shell width 70 mm; both cups right-hand threaded

The Italian answer to BSA, found on classic Italian road frames (Colnago, Pinarello, De Rosa and others) and some frames into the 2010s. Because both cups are normal right-hand thread, the drive-side cup can gradually unscrew itself and must be installed very tight, often with thread retainer.

Why it exists: Italy's national bicycle industry standardized its own metric threading before ISO/BSA became dominant.

Typically found on: Classic and modern-classic Italian road bikes

BB30

2000-late 2010s

Also called: BB30 direct press-fit

42 mm smooth bore; shell width 68 mm (road) or 73 mm (MTB); 6806 bearings (42 x 30 x 7 mm) pressed directly into the frame, retained by circlips

The original oversized press-fit standard: bare cartridge bearings press straight into a machined 42 mm shell, and a 30 mm aluminum crank spindle runs through them. Light and stiff when machined precisely, but unforgiving of tolerance errors — worn or slightly oversized shells creak and eat bearings.

Why it exists: Cannondale developed it (2000) to fit a larger, lighter 30 mm spindle than threaded cups allowed, then opened the standard to the industry in 2006.

Typically found on: Cannondale road and MTB, Specialized (as OSBB variants), many 2008-2016 aluminum and carbon road frames

Square taper (JIS and ISO)

1950s-present (cartridge era ~1990-present)

Also called: Cotterless, Square drive, Taper spindle

Square spindle ends with a 2-degree taper; JIS (Japanese) and ISO (Campagnolo/European) versions differ slightly in taper dimensions; cartridge units sold as shell width x spindle length (e.g. 68 x 113 mm)

The classic crank interface: the crank arm's square hole wedges onto a tapered square spindle end. Modern versions are sealed cartridges that thread into BSA or Italian shells. JIS is by far the most common; ISO cranks (mostly Campagnolo) sit differently on JIS spindles and should be matched to ISO.

Why it exists: Replaced cottered cranks with a simple, cheap press interface; the sealed cartridge (1990s) made it maintenance-free.

Typically found on: Commuters, touring bikes, budget bikes, kids' bikes, and virtually every quality bike made before ~1998

Shimano Octalink

1997-~2006

Also called: Octalink V1, Octalink V2

8-spline hollow steel spindle, ~22 mm diameter; V1 (road, shallow splines) and V2 (MTB, deeper splines) are not interchangeable; threads into BSA shells as a cartridge

Shimano's late-1990s replacement for square taper: a larger hollow splined spindle for stiffness. Short-lived once external-bearing Hollowtech II arrived. If your crank has 8 splines and a Shimano logo, it is Octalink — check V1 vs V2 before buying.

Why it exists: Square taper spindles were the flex and weight bottleneck; splines allowed a fatter hollow spindle.

Typically found on: Shimano Dura-Ace/Ultegra/105 road cranks ~1997-2004 and XT/XTR MTB cranks of the same era

ISIS Drive

1999-~2007

Also called: International Spline Interface Standard

10-spline spindle, ~22 mm diameter; cartridge unit threads into BSA shells; various spindle lengths (108-128 mm)

An open-standard splined interface created by Race Face, Truvativ, and Chris King as the non-proprietary answer to Octalink. Ten splines instead of Shimano's eight. Its small bearings had short lives, which hastened the move to external-bearing designs.

Why it exists: Component makers refused to license Shimano's patented Octalink and built an open alternative.

Typically found on: Early-2000s MTB, BMX, and touring cranks (Race Face, Truvativ, FSA)

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
Shell Standard critical	Names the frame's bottom bracket interface — threaded or press-fit, and which variant. This single value narrows replacement bottom brackets to the correct family.	BSA (English threaded) · BB86/BB92 (PressFit 41) · PF30 · BB30 · T47 · BB90/BB95 (Trek) · BB386EVO · BBright · BB30A/PF30A (Cannondale) · Italian threaded
Shell Width(mm) critical	The face-to-face width of the frame's bottom bracket shell. Combined with the shell diameter, it usually identifies the standard outright and determines which crank spindle lengths and spacers work.	68 · 73 · 86.5 · 92 · 70 · 79 · 83 · 85.5 · 89.5 · 90.5 · 95.5 · 100 · 120
Crank Spindle Interface critical	The bottom bracket's bearings and end fittings must match the crank's axle. A BB86 shell, for example, can take a 24 mm Shimano crank or a SRAM DUB crank — but only with the matching bottom bracket.	Shimano Hollowtech II (24 mm) · SRAM DUB (28.99 mm) · 30 mm (BB30/BB386EVO) · SRAM GXP (24/22 mm) · Square taper JIS · Square taper ISO · Shimano Octalink · ISIS Drive
Shell Inner Diameter(mm) helpful	For smooth press-fit shells, the bore diameter is the most reliable identifier: 37 mm is Trek BB90/95, 41 mm is BB86/92, 42 mm is BB30, 46 mm is PF30/BB386EVO/BBright.	41 · 46 · 42 · 37 · 34.8 (BSA threaded) · 47 (T47 threaded)
Thread Specification helpful	Threaded shells use different threads that are not interchangeable. BSA is by far the most common; Italian appears on older Italian road frames; T47 is the modern large-diameter thread.	1.37 in x 24 TPI (BSA/English) · M47 x 1.0 (T47) · 36 mm x 24 TPI (Italian) · 35 mm x 1.0 (French, legacy)
Spindle Length (square taper/ISIS/Octalink)(mm) optional	Cartridge bottom brackets are sold by shell width plus spindle length (e.g. 68 x 113 mm). The length sets the chainline, so match what the crank maker specifies.	113 · 110 · 107 · 118 · 122.5 · 127 · 103
Bearing Placement optional	External (outboard) cups sit outside the shell faces and allow bigger bearings on threaded frames; internal designs put bearings inside the shell. It affects crank spacer setups and Q-factor.	External (outboard) cups · Internal (inside shell) · Cartridge (sealed unit inside shell)

How to identify which one you have

Threaded or smooth?

Look at the bottom bracket area from below. If you can see wrench notches or splined tool fittings on cups, and threads where cup meets frame, it is threaded (BSA, Italian, or T47). If the bottom bracket is smooth-faced with no tool fittings and appears pressed flush into a smooth bore, it is press-fit. Very large threaded cups (about 47 mm) with 'T47' markings indicate T47.

By measuring

Measure the shell width — the frame's bottom bracket tube from face to face, ignoring any cups sticking out — with a ruler or calipers. Threaded: 68 mm = BSA road, 73 mm = BSA MTB, 70 mm = Italian. Press-fit: measure width AND the inside bore diameter (remove cranks/BB if possible). 41 mm bore + 86.5 or 89.5-92 mm width = BB86/BB92; 42 mm + 68/73 mm = BB30; 46 mm + 68/73 mm = PF30; 46 mm + 79 mm = BBright; 46 mm + 86.5 mm = BB386EVO; 37 mm + 90.5/95.5 mm = Trek BB90/BB95.

By markings

Threaded cups and cartridge units are usually stamped with their spec, e.g. '68 x 1.37 x 24T' (BSA 68 mm) or '36 x 24' (Italian); the shell itself may have the size stamped underneath. Press-fit bottom brackets often print the standard on the cup face ('PF30', 'BB86', 'DUB') or on the visible bearing shield. Crank spindles help too: 'DUB' is printed on SRAM 28.99 mm spindles, and Shimano road/MTB cranks since ~2004 are 24 mm Hollowtech II.

By frame make, model, and year

The fastest route: search your frame's exact make, model, and year plus 'bottom bracket' — manufacturer spec pages list the standard. Rules of thumb: Trek carbon 2007-2019 is usually BB90/BB95 (T47 after ~2019); Cervelo 2011-2019 is BBright; Cannondale is BB30/PF30/BB30A; most 2010s Shimano-spec carbon bikes are BB86/BB92; most steel/aluminum bikes and current mountain bikes are BSA threaded.

By the crankset you own

If you know your crank, you know the spindle the bottom bracket must accept: Shimano since ~2004 = 24 mm; SRAM with 'DUB' on the spindle = 28.99 mm; SRAM GXP = 24/22 mm stepped; Cannondale/FSA/Race Face 30 mm spindles = BB30-style; older cranks pulled with a square hole = square taper; 8 splines = Octalink; 10 splines = ISIS.

Compatibility gotchas

The bottom bracket must match the frame shell AND the crank spindle. Most shells accept several spindle types via different bottom bracket models — e.g. a BSA 68 mm shell can run square taper, 24 mm, DUB, or 30 mm cranks — so specify both when shopping.
Press-fit creaking is usually a tolerance problem, not a fatal flaw. Thread-together bottom brackets (two cups that screw into each other through the shell, from Wheels Mfg, Hope, Chris King and others) cure most creaky PF30/BB86/BB92 frames without frame modification.
30 mm spindle cranks do NOT fit BB86/BB92 or Trek BB90/BB95 frames — the bore is too small for adequate bearings. DUB (28.99 mm) squeaks into BB86/92 with special bearings; BB90/95 accepts 24 mm spindles only.
SRAM GXP and Shimano 24 mm bottom brackets are not interchangeable: GXP's non-drive bearing has a 22 mm bore. Match the bottom bracket to the crank brand.
Square taper JIS (Shimano and almost all Asian cranks) and ISO (Campagnolo and older European cranks) tapers differ slightly; mixing them changes how far the arm seats and affects chainline and arm life.
Italian 70 mm and BSA 68 mm threaded parts are not interchangeable — different thread diameter, and Italian's right-hand drive-side cup can self-loosen; install very tight with retaining compound.
BSA shells wider than 73 mm exist: 83 mm (downhill) and 100 mm (fat bikes) need cranks with correspondingly longer spindles.
Cannondale BB30A/PF30A asymmetric shells need 'A'-specific cranks or spacer kits; standard BB30 road cranks are too short.
Mid-drive e-bikes have no bottom bracket standard — the motor is the bottom bracket. Replace crank arms with ones matching the motor spindle (often ISIS or square taper), and refer motor bearing issues to a dealer.
When in doubt on a press-fit frame, do not force anything: cups are removed and installed with presses, and sloppy installs can wear the bore oversize and make creaking permanent.

References

Related components

Crankset