The Headset connects a frame to a fork and provides the smooth action which is necessary for easy turning and control. Headsets come in a variety of sizes, 1 1/8 Inch being the most popular. Fitments types are also varied from traditional external, integrated and semi integrated. If your headset is feeling notchy or has become loose beyond being adjusted through the top cap adjuster, it may well need replacing. With headsets it is vital to match like-for-like the old and new. For example an integrated headset cannot be fitted to an external headset frame & fork.