page_title: Headset (bicycle part)
section_title: Sizes
hierarchical_section_title: Headset (bicycle part) / Sizes
caption_attribution_description: English: headset classic Italiano: serie sterzo classico
context_page_description: The headset is the set of components on a bicycle that provides a rotatable interface between the bicycle fork and the head tube of a bicycle frame. The tube through which the steerer of the fork passes is called the head tube. A typical headset consists of two cups that are pressed into the top and bottom of the headtube. Inside the two cups are bearings which provide a low friction contact between the bearing cup and the steerer.
context_section_description: Traditional bicycle head tubes and headsets are sized for a 1-inch-diameter (25 mm) steerer tube (also known as the fork column). Many frame and fork manufacturers are now building their parts around a steerer tube with a diameter of 1⅛ inch. The larger diameter of the head tube and headset gives added stiffness to the steering portion of the bicycle.
  Common sizes
  1" or 1 inch (25.4 mm).  This may have a fork crown (The base of the fork steerer tube) of a number of different dimensions.  Milling may be necessary to make some headsets fit.
  26.4 mm (ISO)
  27.0 mm (JIS)
  Other sizes are becoming common, more so all the time.
  1.125" or 1⅛ inch (28.575 mm), originally branded Tioga "Avenger"
  1.25" or 1¼ inch (31.75 mm), originally branded Gary Fisher "Evolution"
  1.5" or 1½ inch (38.1 mm), as used in the OnePointFive International Standard.
  Cannondale Headshok. Although a Headshok steerer is close to 1.5" it is actually 1.5625" or 1 9/16 inch (39.6875 mm). The Headtube dimensions for 1.5" and Headshok are very similar, differing only in the minimum press depth.
  1.5 inch to 1⅛ inch "tapered" headsets (2009 onwards). The lower bearing is 1.5 inches for increased stiffness and the upper is 1⅛ in for reduced weight and to match existing stem interface.
  The stack height of a headset is the total assembled height of the headset components and, in the case of a threadless system, the stem, discounting the tangs which press into the head tube and (in the case of threaded headsets) the thickness of the top seal of the locknut.  The stack height of a frame and fork is the difference between the steerer tube length and the head tube length.  Stack height is critical because a headset with a greater stack height than the frame and fork will not fit; the locknut will not thread on sufficiently (threaded) or there will be no room for the stem (threadless).  If the headset has a lower stack height than the frame and fork, spacers are added to make up the difference.
caption: Threaded headset
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