Fsa is the world leading headset manufacturer and the core of their product line with many years of experience they understand that multiple dimensions and exacting requirements are a must when it comes to headsets the fsa orbit c 33 acb tapered headset is an integrated headset to fit head tubes that are tapered the bearing are 1 18 45 x 45d upper and 1 14 45 x 45d lower angular contact bearings that sit flush in the frame with head tube outer diameter of 47mm upper and 52mm lower on ta