|Steerer O.D in mm||Threads
||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. ISO and other 30.2 mm O.D.cups are a very tight fit into the head tube; best mill it to avoid damage.|
||30.0 mm||27.0 mm||25.4 mm||26||22.2 mm (7/8")||Proprietary size used on Raleighs made in Nottingham, England. ISO and other 30.2 mm O.D, frame cups are a very tight fit into the head tube; best mill to avoid damage.|
|1" ISO Standard
||30.2 mm||26.4 mm
||24||22.2 mm (7/8")||This is the standard 1" size.|
|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" Italian||30.2 mm||26.5 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,
|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
|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.|
||30.8 mm||26.7 mm||26 mm||25.4
|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
|26.4 mm (varies)||25.4 mm||24||21.15 mm
|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
|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,
|33.0 mm||25.4 mm||24||22.2 mm
|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|
|EC32||32.7 mm||26.4 mm||Used mainly on bicycles with one-piece cranks. BMX/O.P.C|
|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.|
|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.|
|Various||52-56mm||Use crown race reducer|
|EC37||37.0 mm||33.0 mm||Mainly used on tandems|
|49.7 mm||39.8 mm||OnePointFive standard for downhill and freeride applications. Press fit|
|IS52||52 mm||39.8mm||Integrated lower headset. Slip fit.|
|ZS55/40||55 mm||39.8mm||Internal, press fit.|
|56 mm||39.8mm||Internal or external, press fit.|
|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.|
Last Updated: by Harriet Fell