Full Speed Ahead FSA Orbit 1.5ZS Tapered Bicycle Zero Stack Headset For tapered 50mm / 62mm OD headtubes Upper head tube 44mm ID - Lower head tube 56mm ID For tapered fork steerer 1.5 to 1-1/8 Alloy top cover with angular contact bearings NO.57 For 44mm/56mm ID Headtube 1.5in to 1 1/8in tapered steerer