The lower bearing is conventional. The upper parts are replaced by a cartridge bearing inside the head tube. The steerer necks down abruptly from a conventional diameter at the bottom to about 15mm where it passes through the cartridge bearing, then again to a short threaded section at the top. A castellated nut preloads the bearings and retains the fork in the frame.titch__16":242kppfx said:How does the headset work?