Bottom bracket standards chart

A bottom bracket fits a frame by two numbers: the diameter of the hole in the frame's shell and the width of the shell, plus whether the hole has threads. Measure those, and the standard stops being a guess. The identifier below does the matching; the chart under it is the whole field on one printable page.

Bore = what calipers read across the opening (thread crests on a threaded shell), mm. Width = shell face to face, mm. Cranks: ● the standard's own BB · ◐ a BB made for this shell that steps down to the spindle · ○ only a few small-bearing designs · — won't fit. "Drive side reverse" = the chainring-side cup tightens counterclockwise. Sources: Park Tool, BikeRadar, Wheels Manufacturing standards charts; check the BB maker's compatibility list before buying.

How do I tell which bottom bracket I have?

Take the crank and the old bottom bracket out, then measure two things with calipers. Width: across the shell from one faced end to the other, not including any cups. Bore: the inside diameter of the opening. On a threaded shell the jaws sit on the thread crests, which is the figure the chart lists. Then look inside: threads, a smooth bore, or grooves for circlips. Those three facts identify every current standard except a few honest ties, which the identifier lists rather than guessing.

Threaded or press-fit: which is better?

A threaded shell holds its cups with threads you can tighten, check and re-tighten. A press-fit shell holds bearings or cups by interference: the hole is made a hair smaller than the part pressed into it. That works beautifully when the hole is right and creaks when it isn't, and a carbon frame's molded bore can't be re-machined like an alloy one. A press fit is only as good as the hole it's pressed into. Press-fit frames were lighter to make and left room for fat 30 mm spindles. The industry's answer to the creaking was T47: a press-fit-sized bore with threads cut into it. Since the late 2010s, brand after brand has moved its road and gravel frames back to BSA or T47. If you're choosing a new frame, we'd take threads.

Why are there so many bottom bracket standards?

Mostly to fit fatter spindles. A bigger spindle is stiffer and lighter for its strength, but it has to pass through a bearing, and the bearing has to sit somewhere between the spindle and the frame. The room for that is simply (bore − spindle) ÷ 2 on each side:

Radial room per side. For scale: a 6806 bearing (30 × 42 mm) is 6 mm thick per side; a 24 × 37 mm bearing is 6.5. A cup adds wall thickness on top.

Read the table and the standards explain themselves. BB30's 42 mm bore leaves exactly 6 mm around a 30 mm spindle, the thickness of a 6806 bearing, so the bearing presses straight into the frame. PF30 widened the bore to 46 mm to leave 2 mm more for a cup. BB86's 41 mm bore was sized for 24 mm spindles, and BB90's 37 mm bore holds a 24 × 37 bearing with nothing to spare.

Which cranks fit my bottom bracket?

Four spindle sizes cover nearly every modern crank: 24 mm (Shimano Hollowtech II and many others), SRAM's older GXP (24 mm stepping to 22 on the non-drive side), SRAM's DUB (28.99 mm), and 30 mm (Race Face, Rotor, Cannondale, FSA and Praxis). The chart's right-hand columns cover every pairing. The pattern is simple: a threaded shell takes nearly any crank, a big (42–46 mm) press-fit bore takes any crank with an adapter bottom bracket, and a small (37–41 mm) bore limits you to 24 mm and DUB. Spindle length is a separate check: wide shells like 386EVO and BBright need cranks with long enough spindles, or spacers to fill a narrower shell. The BB maker's compatibility list settles it.

BSA, T47 and Italian: the threaded ones

BSA (English, ISO) is the default: 1.370″ × 24 TPI, shells 68 / 73 / 83 / 100 mm. Its drive-side cup is reverse-threaded: it tightens counterclockwise, so pedaling can't unscrew it. Turning it the "normal" way to tighten it strips it. T47 uses the same convention with a 47 mm metric thread, sized like a press-fit bore, in narrow shells (external cups) and in 85.5–86.5 mm shells with the bearings inside. Italian threads are 36 mm × 24 TPI in a 70 mm shell, with both cups tightening clockwise. That's why Italian drive cups have a reputation for working loose, and why they deserve thread prep and the full torque. Threaded cups go in at 35–50 N·m; the torque chart has the rest of the drivetrain.

BB86 vs BB30 vs PF30 vs 386EVO: the press-fit alphabet

Press-fits sort by bore first. 37 mm is Trek's BB90 and BB95, with bearings pressed straight into the frame. 41 mm is Shimano's BB86 (road, 86.5 wide) and BB92 (MTB), with bearings in cups. 42 mm is BB30 and its asymmetric BB30A: bearings straight into the frame, held by circlips, so look for the grooves. 46 mm is PF30, PF30A, 386EVO and BB392EVO: a smooth bore that takes cups, told apart by width (68, 73, 86.5, 91.5). Cervélo's BBright is 79 mm wide in either bore. Every 46 mm shell can take any modern crank with the right bottom bracket; 37 and 41 mm shells stop at 24 mm and DUB.

Can I fix a creaking press-fit bottom bracket?

Usually, without changing the frame. Most creaks come from the fit between cup and bore, so the fixes aim there: a clean install with the right retaining compound, then a thread-together press-fit BB, where the two cups screw into each other through the shell and clamp from both sides instead of relying on interference alone. If a bore is truly oversized or oval, a shop can measure it; on a carbon frame the options narrow to sleeves or the manufacturer. What you can't do is turn a press-fit shell into T47: the standard lives in the frame. Before chasing the BB, rule out the usual impostors: pedals, cleats, chainring bolts, the seatpost and the saddle rails all creak in time with pedaling.