The Box Two Hollow Center Clamp stem is cold forged from the highest quality 6061-T6 aluminum available. Featuring an open skeletal design & a dual mid-bolt wedge mounting system, they are lightweight yet maintain a very high level of strength. A 53mm extension stem weighs just 218g/7.7oz. By removing the rear pinch bolts & moving the mounting bolts to the middle of the stem, Box reduced the weight & E3size & eliminated a serious hazard to the rider’s knees. These stems come with either a 48mm or 53mm extension & have a 22.2mm clamping diameter. To ensure proper clamping force, the stem must be mounted on a fork with at least 45mm of exposed steerer tube. Not compatible with forks that have carbon fiber steerer tubes. section Product Specs TYPE: Front Load REACH: 40mm/45mm/48mm/53mm RISE: 5mm CLAMPING DIAMETER: 22.2mm WEIGHT: 218g/7.7oz (53mm) E4