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 xtreme pro 15 headset is a conventional threadless headset has forged and cnc machined from 7075t6 aluminium cups which is made to fit frames with 55mm od head tubes with 15 steerer the bearings are a 15 industrial bearing and the crown race is alloy