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Sheldon Brown's Bicycle Headset Dimension Crib Sheet

Threaded Headsets/Steerers
Size
Steerer O.D.
Stem diameter
Steerer I.D.
Crown race
Inside diameter
Frame Cup
Outside Diameter
Threads
Per inch
Notes
BMX/ O.P.C. bikes .833"
(21.15 mm)
26.4 mm 32.7 mm 24 Used mainly on bicycles with one-piece cranks, also some early mountain bikes.
French 25 mm 22 mm 26.5 mm,
27.0 mm
30.2 mm 25.4
(1 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. Interchangeability note: These 5 sizes of forks and headsets all fit the same frames, since the head tube size is the same.
1" ISO Standard
(25.4 mm)
7/8" (22.2 mm) 26.4 mm 30.2 mm 24 This is the standard 1" size.
1" Italian (25.4 mm) 7/8" (22.2 mm) 26.5 mm,
27.0 mm
30.2 mm 24 Obsolete. Threads are cut at 55 degrees, but an ISO or J.I.S. top headset can be used. Note possible difference in crown race press-fit diameter.
1" J.I.S.
(25.4 mm)
7/8" (22.2 mm) 27.0 mm 30.0 mm 24 Older or lower-quality bicycles from Asia. 0.2 mm discrepancy may result from measuring the I.D. of the head tube (press fit).
1" Raleigh
(25.4 mm)
7/8" (22.2 mm) 26.4 mm 30.2 mm 26 Proprietary size used on Raleighs made in Nottingham, England
Austrian
(26 mm)
22 mm 26.7 mm 30.8 mm 25.4
(1 mm)
Higher quality Austrian bikes use English/ISO.

East German (DDR) 22 mm 26.8 mm 30.6 mm 26 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.
French Tandem28 mm 22 mm     25.4
(1 mm)
Obsolete and rare.
1 1/8" (28.6 mm) 1" (25.4 mm) 30.0 mm 34.0 mm 26 "Oversized" (This size is more often used for threadless systems.)
1 1/4" (31.8 mm) 1 1/8" (28.6 mm) 33.0 mm 37.0 mm 26 Mainly used on tandems
Threadless Headsets/Steerers
Size/Stem diameter
Steerer O.D.
Crown race
Inside diameter
Frame Cup
Outside Diameter
Notes
BMX/O.P.C 26.4 mm 32.7 mm Used mainly on bicycles with one-piece cranks.
1" ISO Standard (25.4 mm) 26.4 mm 30.2 mm This is the standard 1" size.
1 1/8" (28.6 mm) 30.0 mm 34.0 mm Most newer mountain bikes use this size.
1 1/4" (31.8 mm) 33.0 mm 37.0 mm Mainly used on tandems
1.5" (38.1 mm) 39.8 mm 49.6 mm Proposed OnePointFive standard for downhill and freeride applications.

Spoke Divider

Spoke Divider

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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This page is intended as a quick reference primarily for the benefit of folks in the bicycle business. Feel free to print it out, but please don't reproduce it without proper credit and linkage.

Spoke Divider

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