Cutting the steerer tube to its minimum length prevents switching to a taller stem or to a headset cups with a higher stack height. Any increase in handlebar height after this cut requires purchasing a new fork, a stem with more angular rise (some stems can be turned over for greater height), or a special adapter that clamps onto the steerer tube and gives a higher clamping position for the original stem. In addition, many riders who may have less flexibility than a seasoned racer may wish to gain more height on the handlebars, reducing the saddle-to-handlebar drop and providing a more upright and comfortable riding position. If an owner simply wishes to replace the headset with one having a slightly larger stack height, it may be possible for a bike shop or framebuilder to mill or re-face the head tube to gain an extra 1-2mm of stack height without having to replace the fork. Many threadless fork steerer tubes are cut longer than necessary to allow for adjustments and the steerer tube above the stem is stacked with spacers that can be moved above or below the stem to fine-tune the handlebar height. Often these spacers are aluminum or carbon fiber, but titanium spacers are also available.