Cook Bros Racing Threadless ABEC5 HeadsetAt the heart of the Cook Bros. Racing threadless headset are two super smooth, 4545, sealed bearings. A split aluminum crown race makes installation and removal from forks super easy. But there is more! Despite this being a threadless headset with cups, the 45x45 bearings also work in integrated headset applications. Toss the cups, pop the bearings in your new frame, and roll!