Short answer: you need two pieces of information, not one. The shell standard of your frame (BSA, BB86, BB30, PF30, T47 and so on) and the spindle standard of your crank (24mm Hollowtech II, SRAM DUB, GXP, 30mm, square taper). The bottom bracket is the part that joins those two. Knowing only one of them is why most people order the wrong item.
Contents
- Why you need two measurements
- How to identify your frame shell
- Threaded shells: BSA, Italian, T47
- Press-fit shells: BB86, BB30, PF30 and the rest
- Crank spindle standards
- The lookup: shell + spindle = bottom bracket
- Square taper: JIS, ISO and spindle length
- Press-fit creaking, and the adapter fix
- Common mistakes
- FAQ
Why you need two measurements
A bottom bracket is an adapter. On one side it has to fit the hole in your frame. On the other it has to hold your crank's spindle. Those two things evolved separately and neither one implies the other.
This is why "I have a BB86 frame, which bottom bracket do I need?" has no single answer. A BB86 frame takes a Shimano 24mm bottom bracket, a SRAM DUB bottom bracket, or a 30mm bottom bracket — completely different parts, all correct, depending on what crank you're fitting.
So before ordering, write down both:
- Frame shell: width in mm, internal diameter in mm, threaded or not
- Crank spindle: diameter in mm, or the crank model
How to identify your frame shell
With the crank and bottom bracket removed, you need two numbers and one yes/no.
| What to check | How | What it tells you |
|---|---|---|
| Threads present? | Look inside the shell for a machined thread | Threaded (BSA, Italian, T47) or press-fit |
| Shell width | Measure across the frame, face to face | 68, 70, 73, 79, 86.5, 89.5, 91.5, 92 or 95.5mm |
| Internal diameter | Measure across the opening | 34.8, 36, 37, 41, 42, 46 or 47mm |
Those three answers identify almost every shell in use. The table below decodes them.
Threaded shells
| Standard | Shell width | Thread | Found on |
|---|---|---|---|
| BSA (English, BSC) | 68mm road, 73mm MTB | 1.37″ × 24 TPI | The most common threaded standard worldwide |
| Italian | 70mm | 36mm × 24 TPI | Older Italian frames; rare on new bikes |
| T47 | 68, 77, 85.5 or 86mm | M47 × 1.0mm | Modern frames wanting threaded reliability at press-fit diameter |
The BSA detail that catches people: the drive-side cup is reverse threaded. To remove it you turn clockwise, not anticlockwise. The non-drive side is conventional. This exists so pedalling forces tighten the cups rather than loosening them, and it is the single most common reason someone concludes their bottom bracket is seized when it isn't.
Italian shells have conventional threads on both sides, which is precisely why Italian bottom brackets have a reputation for working loose.
T47 is the interesting one. It takes the 46mm-ish internal diameter that press-fit frames introduced and puts threads on it. You get the bearing spacing and spindle clearance of press-fit with the serviceability of a threaded shell. Several manufacturers have moved to it after a decade of press-fit creaking complaints.
Threaded options in the catalogue: Shimano Ultegra SM-BBR60 and Tiagra BB-RS501 for 24mm Shimano cranks, SRAM English Thread DUB and GXP Team for SRAM, and SRAM DUB T47 or the CeramicSpeed T47/86 for T47 frames.
Press-fit shells
Press-fit means the bearings or their cups are pressed into an unthreaded frame shell. Cheaper to manufacture, lighter, and allows a wider shell for better bearing spacing. The trade-off is that tolerances have to be exact, and when they aren't, the bike creaks.
| Standard | Internal Ø | Shell width | Notes |
|---|---|---|---|
| BB86 (road) | 41mm | 86.5mm | Cups pressed in, 24mm spindle. Very common. |
| BB92 (MTB) | 41mm | 91.5–92mm | Same as BB86, wider shell |
| BB30 | 42mm | 68mm road, 73mm MTB | Bearings press directly into frame. 30mm spindle. |
| PF30 | 46mm | 68mm road, 73mm MTB | Bearings sit in cups, cups press in. 30mm spindle. |
| BB386EVO | 46mm | 86.5mm | PF30 diameter, BB86 width |
| BBRight | 46mm | 79mm asymmetric | Cervelo. Wider on the non-drive side only. |
| BB90 / BB95 | 37mm | 90.5 / 95.5mm | Trek. Bearings press directly into frame. |
| OSBB | 42mm or 46mm | 68mm | Specialized. Carbon frames behave like BB30, alloy like PF30. |
BB30 versus PF30 is the distinction people miss. Both are for 30mm spindles. BB30 presses bare bearings into a 42mm shell; PF30 presses cups containing the bearings into a 46mm shell. They are not interchangeable and the parts look superficially similar in listings.
Press-fit options here: Shimano Ultegra SM-BB72 and GRX BB-RS500-PB for BB86/92, SRAM Pressfit 30, SRAM DUB BB30, CeramicSpeed EVO386 for BB386EVO, and SRAM BBRight DUB 79-A for Cervelo frames.
Crank spindle standards
| Spindle | Diameter | Used by |
|---|---|---|
| Hollowtech II | 24mm | All modern Shimano road and MTB cranks |
| SRAM DUB | 28.99mm | Current SRAM road and MTB |
| SRAM GXP | 24mm drive / 22mm non-drive | Older SRAM. Stepped — not a plain 24mm. |
| 30mm | 30mm | Rotor, Race Face Cinch, FSA386EVO, Praxis, Cannondale Hollowgram |
| Square taper | Tapered square | Older and entry-level cranks. JIS or ISO — see below. |
| Octalink / ISIS | Splined | Legacy. Octalink is Shimano; ISIS is an open standard. |
GXP deserves a flag. It looks like a 24mm spindle and it is on the drive side, but the non-drive end steps down to 22mm and the crank arm seats against a shoulder. A plain 24mm bottom bracket will not correctly locate a GXP crank.
The lookup: shell + spindle = bottom bracket
Find your frame shell in the left column and your crank across the top.
| Frame shell | Shimano 24mm | SRAM DUB | SRAM GXP | 30mm |
|---|---|---|---|---|
| BSA 68/73 | Threaded Hollowtech II BB | DUB BSA | GXP English thread | Threaded 30mm BB |
| T47 | T47 for 24mm | DUB T47 | T47 GXP | T47 for 30mm |
| BB86 / BB92 | BB86/92 press-fit | DUB PF 86.5 / 92 | GXP press-fit | Not directly — 41mm shell too small |
| BB30 | BB30 with adapter cups | DUB BB30 | GXP BB30 adapter | BB30 bearings direct |
| PF30 | PF30 to 24mm adapter | DUB PF30 | GXP PF30 | PF30 cups |
| BB386EVO | 386 to 24mm adapter | DUB EVO386 | GXP 386 | 386EVO direct |
| BBRight | BBRight to 24mm | DUB BBRight | GXP BBRight | BBRight 30mm |
Where the table says "adapter," that means a bottom bracket designed to reduce a larger shell down to a smaller spindle. This is normal and reliable, not a bodge — fitting a 24mm Shimano crank into a PF30 frame is one of the most common combinations on the road.
Square taper: JIS, ISO and spindle length
Square taper is still everywhere on entry-level and older bikes, and it has two variables people overlook.
JIS versus ISO. Two taper specifications exist. JIS is the Japanese standard used by Shimano and most Asian manufacturers, and it is what you'll find on the overwhelming majority of bikes in India. ISO is the older European specification, used by Campagnolo and some Italian and French cranks.
They are not interchangeable. The tapers differ enough that an ISO crank on a JIS spindle sits further on than intended, and a JIS crank on an ISO spindle sits further off — which changes your chainline and, in the worst case, lets the crank work loose and destroy the taper.
Spindle length. Square taper bottom brackets come in specific lengths — commonly 107, 110, 113, 118, 122.5 and 127.5mm — and the correct one is determined by your crank model and the chainline it needs. There is no universal length. Check what your crank manufacturer specifies before ordering, because a spindle 5mm too long or short will shift your chainline enough to cause poor shifting and chain rub.
Square taper units here: Shimano BB-UN300, Tange Seiki LN3912, Tange Seiki 21E, and Chin Haur CH52-68 for 68mm shells or CH52-73 for 73mm.
Press-fit creaking, and the adapter fix
A creaking press-fit bottom bracket is usually not the bearings. It's the interface between cup and frame, where a tolerance mismatch of a few hundredths of a millimetre lets the parts move minutely under load.
Things that genuinely help, in order of how often they work:
- Reinstall with retaining compound or assembly grease. A dry press fit into a slightly oversized shell will creak. Do not install press-fit cups dry.
- Confirm the frame shell is faced and within tolerance. Carbon frames in particular can come out of the mould slightly out of round.
- Check it isn't actually the crank interface, pedals, or seatpost. Creaks transmit through a frame and the bottom bracket gets blamed for all of them. Isolate before replacing.
- Convert to threaded. A PF30-to-BSA adapter threads a BSA shell into a PF30 frame. You then run a normal threaded bottom bracket. This is the permanent fix for a frame that creaks no matter what you press into it, and it means every future bottom bracket is a simple threaded part.
If you'd rather cover several standards with one part, the Token Ninja TF37 is designed to fit multiple shell types with interchangeable adapters.
Common mistakes
Ordering by frame standard alone. "BB86 bottom bracket" is not a complete specification. BB86-for-Shimano and BB86-for-DUB are different parts.
Turning the drive-side BSA cup the wrong way. It's reverse threaded. Turning it anticlockwise tightens it further and can strip the shell.
Assuming BB30 and PF30 are the same because both take 30mm cranks. Different shell diameters, different parts.
Treating GXP as plain 24mm. The stepped non-drive side means it needs GXP-specific bearings.
Guessing square taper spindle length. It's determined by the crank, not the frame. Get the number from the crank manufacturer.
Pressing cups in without the right tool. A press-fit bottom bracket must go in square. Hammering one in with a block of wood will cock it, damage the shell, and guarantee a creak.
FAQ
Which bottom bracket do I need for a 68mm BSA threaded shell with a square taper crank?
A threaded BSA square taper bottom bracket in 68mm, with the spindle length your crank specifies. Confirm whether your crank is JIS or ISO taper first — in India it is almost always JIS. The Shimano BB-UN300 and Tange Seiki units cover this combination.
Is the bottom bracket reverse threaded?
On a BSA shell, the drive-side cup is reverse threaded and the non-drive side is conventional. On an Italian shell, both sides are conventional. T47 follows the BSA convention with a reverse-threaded drive side.
What's the difference between BB30 and PF30?
Shell diameter and how the bearings mount. BB30 is a 42mm shell with bearings pressed directly into the frame. PF30 is a 46mm shell where the bearings sit inside cups that are pressed in. Both take 30mm spindles but the parts are not interchangeable.
Can I fit a Shimano crank in a press-fit frame?
Yes. BB86 and BB92 frames are designed around the 24mm Shimano spindle. For PF30, BB386EVO or BBRight frames you need a bottom bracket that adapts the larger shell down to 24mm, which is a standard product rather than a workaround.
Why does my press-fit bottom bracket creak?
Usually the cup-to-frame interface rather than the bearings. Reinstalling with retaining compound solves it in many cases. If the frame shell is out of tolerance and creaks regardless, a PF30-to-BSA adapter converts it to a threaded shell permanently.
Can I convert a press-fit frame to threaded?
If it's a PF30 shell, yes — a threaded adapter presses in once and gives you a BSA shell from then on. BB86 and BB90 shells are too small in diameter for this, so the option isn't available there.
What is T47 and should I care?
T47 is a threaded shell at roughly press-fit diameter — 47mm threads instead of BSA's 34.8mm. It gives the bearing spacing and spindle clearance that press-fit was designed for, while remaining serviceable with tools rather than a press. If your frame has it, it's a good thing.
How do I know if my crank is GXP or DUB?
Measure the spindle. DUB is 28.99mm and constant along its length. GXP is 24mm at the drive side and steps down to 22mm at the non-drive end. If the spindle changes diameter, it's GXP.
Do I need a special tool?
For threaded bottom brackets, an external cup socket — the Birzman Hollowtech II socket covers Shimano and most others. For press-fit you need a press for installation and a drift for removal. Press-fit is genuinely worth having done by a workshop unless you own the tools.
Last updated: August 2026.
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