With semi-integrated cups top and bottom, the SX Pro fits seamlessly into tapered headtubes with a 50mm outside diameter at the top and a 61mm diameter at the bottom. It's designed for a 1 1/8-1.5in tapered steerer tube. Sealed cartridge angular contact bearings are used top and bottom for long-lasting, smooth-running performance with minimum maintenance. Construction is all aluminium, with a forged upper cup and CNC machined lower, contributing to an impressively low weight. Lower 1.5in 36 degrees/ 45 degrees ACB black seal . Stack Height 18.8 2.4=21.2mm. Weight 110.2g 1-1/8in / 1.5in, 36 degrees/ 45 degrees ACB For tapered 50mm / 61mm OD head tube For 1-1/8in to 1.5in tapered fork Forged alloy upper cup with CNC machined alloy lower cup Upper 36 degrees/ 45 degrees ACB blue seal