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Sheldon Brown's Bicycle Headset Dimension Crib Sheet


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Threaded Headsets/Steerers
in order of frame cup outside diameter, crown race inside diameter, steerer O.D., and threads per inch --
the dimensions which affect headset compatibility with frame and fork.
Crown race seat of fork can be milled smaller, frame bearing seats milled larger.

Standard Frame Cup
Outside Diameter
Crown race
Inside diameter
Steerer O.D in mm Threads
Per inch
Stem diameter,
Steerer I.D.
Notes
1" ISO Standard
30.0 mm 26.4 mm
(varies)
25.4 mm
(varies)
24 22.2 mm (7/8") This is the standard 1" size.
1" J.I.S.
30.0 mm 27.0 mm 25.4 mm 24 22.2 mm (7/8") Older or lower-quality bicycles from Asia.
1" Professional/
Campagnolo
30.2 mm 26.4 mm
25.4 mm 24 22.2 mm (7/8") Obsolete. Threads are cut at 55 degrees, but an ISO or J.I.S. top headset can be used.
1" Raleigh
30.2 mm 26.4 mm 25.4 mm 26 22.2 mm (7/8") Proprietary size used on Raleighs made in Nottingham, England
French 30.2 mm 26.5 mm,
27.0 mm
25 mm 25.4
(1 mm)
22 mm Obsolete. French steerers usually have a flat filed on the back, rather than a grooved keyway as with other threaded systems. The bottom headset parts wear faster; you can replace them with ISO parts and use the old top headset.
1" Italian 30.2 mm 26.5 mm,
27.0 mm
25.4 mm 24 22.2 mm (7/8") Obsolete. Threads are cut at 55 degrees, but an ISO or J.I.S. top headset can be used.
East German (DDR) 30.6 mm 26.8 mm
(1 1/8")
26 mm 26 22 mm Very similar to or the same as Austrian. 0.2 mm discrepancy may result from measuring the I.D. of the head tube (press fit). See page on German site.
Austrian
30.8 mm 26.7 mm 26 mm 25.4
(1 mm)
22 mm Higher quality Austrian bikes use English/ISO.

BMX/ O.P.C. bikes 32.7 mm
(varies)
26.4 mm (varies) 25.4 mm 24 21.15 mm
(.833")
Used mainly on bicycles with one-piece cranks, also some early mountain bikes.
French Tandem Let us know, if you do! 28 mm Let us know, if you do! 25.4
(1 mm)
22 mm Obsolete and rare.
1 1/8" 34.0 mm 30.0 mm 28.6 mm 26 25.4 mm (1") "Oversized" (This size is more often used for threadless systems.)
Moulton 30 mm top,
36.4 bottom
33.0 mm 25.4 mm 24 22.2 mm
(7/8")
Moulton Mark III and earlier. Top headset is standard ISO.
1 1/4" 37.0 mm 33.0 mm 31.8 mm 26 28.6 mm (1 1/8") Mainly used on tandems
Threadless Headsets/Steerers
Size/Stem diameter
Steerer O.D.
Frame Cup
Outside Diameter
Crown race
Inside diameter
Notes
BMX/O.P.C 32.7 mm 26.4 mm Used mainly on bicycles with one-piece cranks.
1" ISO Standard (25.4 mm) 30.2 mm 26.4 mm This is the standard 1" size.
1 1/8" (28.6 mm) 34.0 mm 30.0 mm Most newer mountain bikes use this size.
1 1/4" (31.8 mm) 37.0 mm 33.0 mm Mainly used on tandems
1.5" (38.1 mm) 49.6 mm 39.8 mm Proposed OnePointFive standard for downhill and freeride applications.

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Handlebar dimensions
Stem Clamp
Size
Grip Area
Size
Application
22.2 mm 7/8" 22.2 mm 7/8" Steel bars. Mainly BMX, older Mountain bike bars.
23.8 mm 15/16" 22.2 mm 7/8" Obsolete British size for steel handlebars, common on older 3-speeds.
This size was also used for older British steel drop bars.
25 mm 23.5 mm Obsolete French size.
25.4 mm 1" 22.2 mm 7/8" Standard I.S.O. size, used on the vast majority of newer bicycles with upright handlebars.
This size was formerly common for steel drop bars.
25.4 mm 1" 23.8 mm 15/16" Standard I.S.O. size, used on most bicycles with drop handlebars.
Also used on older British aluminium upright handlebars.
25.8 mm 23.8 mm 15/16" Unofficial in-between size used by some Italian handlebar makers for handlebars designed to be usable in either ISO (25.4) or Italian (26.0) size stems.
26.0 mm 23.8 mm 15/16" Italian standard for drop bars, other bars made to fit Italian stems and some high-end aftermarket drop bars.
This is sometimes incorrectly called "road" size.
26.4 mm 23.8 mm 15/16" Older Cinelli and Cinelli copies. Cinelli changed over to 26.0 mm in 1998.
27 mm 23.8 mm 15/16" Titan (obsolete).
31.8 mm 1 1/4" 23.8 mm 15/16" Road oversized.

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