Internal headsets are available for 1 1/8”, 1 ¼”, 1.5”, and tapered steerer tubes. Internal headsets are sometimes referred to as Zero Stack (ZS) because both cup and bearing is housed entirely inside the headtube.
Alloy top cap
For 49mm OD headtube
Chromoly cups with intergrated semi-cartridge bearing
Buy FSA No.11N Headset from Chain Reaction Cycles, the World’s Largest Online Bike Store.