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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" 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. Can be milled to ISO standard.
1" ISO Standard
30.2 mm 26.4 mm
25.4 mm
24 22.2 mm (7/8") This is the standard 1" size.
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 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
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. Fork can be milled to ISO.
French 30.2 mm 26.5 mm,
27.0 mm
25.0 mm 25.4
(1 mm)
22.0 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.
East German (DDR) 30.6 mm 26.8 mm
(1 1/8")
26 mm 26 22.0 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)
22.0 mm These are found on bicycles sold by Sears, made by Steyr in Austria. Higher quality Austrian bikes use English/ISO.
BMX/ O.P.C. bikes 32.6 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 now, if you do! 25.4
(1 mm)
22.0 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 30.2 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
Stem
I.D.,
Steerer
O.D.
SHIS
term
Frame Cup/
Cartridge
Outside
Diameter
Crown race
Inside
diameter
Notes
21.15 mm
(0.833")
EC32 32.7 mm 26.4 mm Used mainly on bicycles with one-piece cranks. BMX/O.P.C
1"
(25.4 mm)
IS38 38.0 mm 26.4 mm Slip fit, 36° angular contact at bottom of bore.
EC30 30.2 mm 26.4 mm This is the ISO standard 1" size.
1 1/8"
(28.6 mm)
EC34 34.0 mm 30.0 mm Most newer mountain bikes with external cups use this size.
IS41 41.0 mm Integrated, angular contact, slip fit.
ZS41 41.3 mm Low profile, press fit. May have cartridge or cup-and-cone bearings.
  41.6 mm Integrated, angular contact. Obsolete.
IS42 41.8 mm Integrated angular contact; Campagnolo Hiddenset
  41.9-42.0 mm Microtech integrated, press fit, square-bottomed recesses. Obsolete
ZS44 44.0 mm Retainer/loose balls or cartridge, which is slip fit into pressed cup
  44.0 mm Integrated, 36° angular contact. Obsolete
IS47 47.0 mm Integrated lower only, slip fit.
1 1/4"
(31.8 mm)
EC37 37.0 mm 33.0 mm Mainly used on tandems
1.5"
(38.1 mm)
EC49,
ZS49
49.7 mm 39.8 mm OnePointFive standard for downhill and freeride applications. Press fit
52 mm
(2.05")
IS52 52 mm ? Integrated lower headset. Slip fit.
56 mm
(2.21")
EC56,
ZS56
56 mm ? Internal or external, press fit.

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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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