Headset for Tapered steerer tube forks, used in Tapered Headtube frames -1 1/8 upper steerer size -1.5 lower steerer size -45/45 ACB Upper bearing (42mm OD) -36/45 ACB Lower bearing (51.8mm OD) -Alloy Top Cap -9mm Stack height Designed for tapered steerer FSA Part number 121-0466A Not sure if this is the one you need? Check out the handy FSA Headset ID Tool here http://www.fsaeasyheadset.com/