This lightweight aluminum crown race has an integral mold seal that keeps it clean. It is compatible with 10-, 40- and 110-Series headsets and backwards compatible with S and XX Series, 52mm lower headset bearings, and 40mm (1-1/2") tapered steerer tubes. Features: Integral mold seals keep out the elements Lightweight aluminum construction Compatibility: 10-, 40- and 110-Series headsets and backwards compatible with S and XX Series, 52mm lower headset bearings, & 40mm (1-1/2") tapered steerer tubes Crown Race: 40