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 no 51 semi integrated tapered headset is a semi integrated headset that is design to fit 51 to 62mm outside diameter tapered head tubes you can use no51 with 1 14 to 15 tapered forks the bearings are 1 14 top and 15 lower angular contact bearings and with a 1