Headset for Tapered steerer tube forks, used in Tapered Headtube frames -1 1/8 upper steerer size -1 1/4 lower steerer size -45/45 ACB Upper bearing (42mm OD) -45/45 ACB Lower bearing (47mm OD) -Carbon top cap -8.7mm Stack height Designed for tapered steerer FSA Part Number 121-0474 Not sure if this is the one you need? Check out the handy FSA Headset ID Tool here http://www.fsaeasyheadset.com/