Traditional threadless headsets are available to fit 1” and 1 1/8” steerer tubes. Traditional headsets are pressed into the headtube and have two external cups that house the bearings.
INTERNAL / ZS STYLE
Internal headsets are available for 1 1/8”, 1 ¼”, 1.5”, and tapered steerer tubes. Internal headsets are sometimes referred to as Zero Stack (ZS) because both cup and bearing is housed entirely inside the headtube.
Integrated Headsets are similar to Internal with the exception that the bearing does not rest inside a bearing cup. The bearing is set directly into the headtube and usually does not require special press tool to install. There are a few types of Integrated headsets, sometimes referred to as Cane Creek Standard, Campy Standard, or TH standard. It is important to measure the inside diameter of the headtube correctly in order to be certain the correct integrated headset is being used in the frame.
One point five headsets fit steerer tubes that are 1.5” in diameter. There are models that are Traditional threadless or Internal. The internal diameter of the headtube determines if the frame is compatible with traditional or internal 1.5” headsets.
Tapered headsets are a combination of the other styles. Usually a tapered steerer tube will have a 1 ¼” or 1.5” lower diameter, and a 1 1/8” upper diameter. The headsets for these frames & forks can be any combination of traditional, internal, or integrated headsets. It is very important to accurately measure the inner diameter of the headtube top and bottom to narrow down the headset model needed. In some cases, Tapered headtubes can be used with a straight 1 1/8” steerer tube if a reducing headset race is used.
Threaded headsets are for use with 1″ threaded steerers and are a traditional headset. Threaded Headsets are pressed into the head tube and have two external cups that house caged balls or bearings, and a top locknut to fix the headset.
An Angle headsets is a new internal headset model which gives the rider the option to adjust their headset angle. It works only with 1 1/8” fork steerers but it is usable on both straight or tapered headset tube. The angle variation is made by the bearings position in the cup. The bearings adjust to different angles and headtube lengths due to the spherical contact surface between bearing and its seat.