"Not compatible with carbon fiber steerer tube forks" Hollow stems are cold forged from the highest quality 6061-T6 aluminum available. Featuring an open skeletal design and a dual mid-bolt wedge mounting system, they are lightweight yet maintain a very high level of strength. A 53mm extension stem weighs just 218 grams/7.7 ounces. By removing the rear pinch bolts and moving the mounting bolts to the middle of the stem, we reduced the weight and size and eliminated a serious hazard to the rider’s knees. These stems come with either a 48- or 53mm extension and a 22.2mm bar bore. To ensure proper clamping force, the stem must be mounted on a fork with at least 45mm of exposed steerer tube.