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Sheldon Brown's Unthreaded Bicycle Bottom Bracket Crib Sheet

(See also my Threaded Bottom Bracket Dimensions Cribsheet and Bottom Bracket Size Article)

This file updated by John Allen, April 2014

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At the 2011 Interbike show, Calvin Jones of Park Tool sighed as he described the proliferation of new bottom-bracket dimensions. I've covered all the ones here which I can find, and listed them in order of bottom-bracket shell internal bearing seat diameter so as to highlight compatibilities. Some are obscure or no longer in use. Adapters for some -- ranging from the venerable Ashtabula system to new high-end systems -- allow use with a variety of spindles. Phil Wood makes adapters to fit most press-fit bottom brackets: "[i]f you have a press fit bottom bracket (Merlin, Klein, Fisher, Ritchey, Fat Chance) and need replacement parts, we have spindles and bearings that will work" -- see Phil Wood FAQ page on bottom brackets. Wheels Manufacturing makes a number of adapters between these systems, and FSA makes some. Also see compatibility information in the table below . -- John Allen.

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Standard: Threading or press fit Adjustable
Merlin 30 mm pressed     68 mm  
Thompson/Thun 30, 33, 35, 40, 45 mm pressed left (cone and locknut) right (cone and locknut) 65, 68,70 mm 2-piece or 3-piece crank. Cup and cone bearings. No shoulder inside shell; loose tolerances.
Mavic/Stronglight 1.375" (or 35 mm) beveled     65-73 mm Bottom bracket cartridge clamps into a conventional BB shell once the ends have been faced with a 45-degree taper. Can work with English, ISO, French or Raleigh. Italian?
Velo Orange threadless 1.375" (or 35 mm), threaded or unthreaded w/o shoulders     68 mm Clamps into bottom-bracket shell using expanding sleeves. but not Italian threaded BB shell unless possibly with a steel shim, 0.20"/0.5mm
Fat Chance/Gary Fisher 35 mm pressed     68 or 73 mm Circlips on grooves in axle outboard of bearings
Klein 35 mm pressed     68 mm Like Fat Chance/Gary Fisher but no axle circlip
Ritchey 35 mm pressed     68 mm Same bearing as Fat Chance/Gary Fisher
Shimano Hollowtech II, FSA MegaExo, RaceFace X-type 37 mm pressed or British/ISO threaded ISO right ISO left 90 mm, 95 mm including cups External cups for cartridge bearings fit British/ISO threaded bottom brackets or unthreaded shell. 24 mm spindle, spacer to use 6805 bearings with 25mm I.D.. Bottom bracket shell must be faced so cups are parallel.
BB90/BB95 37 mm     90 mm, 95 mm Used on Trek Madone carbon frames. 24 mm spindle.
Spanish 37 mm press fit       19, 20, 22 mm spindle
Mid 41 mm press fit       19, 20, 22 mm spindle
BB83/BB86, BB92 41 mm press fit     86, 92 mm 19 mm or 24 mm spindle
Thun-BB30 42 mm press fit     68, 73 mm Plastic cups retained by shoulders, like PF30. Can fit BB30 bore but not vice versa.
BB30, Cannondale System Integration 42 mm press fit     68, 73 mm Adapters allow use with various 30 mm spindles.
BBRight Direct Fit 42 mm press fit     79 mm Asymmetrical: 34mm center to right. 30 mm spindles
Swedish OPC 45 mm external external ?  
Specialized OSBB Aluminum 42 mm     68mm See compatibility guide. Usable with several BB30 spindles with Wheels Mfg. adapters
Roadmaster child's 43 mm     65 mm  
Specialized OSBB Carbon 46 mm     61 mm See compatibility guide. Adapters increase shell width to 68 mm. Usable with several BB30 spindles with Wheels Mfg. adapters
Pressfit 30 (PF30) 46mm slip fit     68, 73 mm 30 mm OD spindle; plastic retainer for cartridges.
BBright Press Fit 46 mm     79 mm Asymmetrical: 34mm center to right. Adapters allow use of various spindles.
BB386EVO 46 mm press fit     86.5 mm Like PF30 but wider and with press-fit bearings. See info from FSA Web site. (archived).
ISIS Megatech 48 mm pressed     68 mm  
FSA Megatech 50 mm pressed     68, 73, 83 mm  
Phil Wood American Isis (comments) 50 mm right left   1.5 mm thread pitch.

Ashtabula, O.P.C.

51.3 mm (2.02") i.d.

Male threads
on crank are
24 tpi (most)
28 tpi

left (cone and locknut) right (cone and locknut)
68 mm (2.68") wide
Older U.S. bikes, BMX, Juvenile bikes,
Department store bikes.
24 tpi cranks use #66 retainers, with 10 5/16" balls.
28 tpi cranks use #64 retainers, with 9 5/16" balls.

Note: Some higher quality(mostly BMX) bikes used Tange 24 tpi bottom brackets with #64 retainers.

Eccentric 54 mm     68 mm For tandems and single-sprocket drive with vertical dropouts or belt drive. May be split with pinch bolts, or have setscrews. Shell diameter not critical, internal dimensions for bottom bracket may vary. Also see Gary Fisher Eccentric below.
Gary Fisher Eccentric 57 mm     73 mm Also see Eccentric above.

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Chainline Dimensions (See also my Chainline Article )

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