FSA IS-2 UPPERAN UPPERCUTHeadsets can be a tricky thing to navigate. Many different bikes can use many different headset standards. The FSA IS-2 Upper is a replacement headset upper from FSA. It is designed to fit 1-1/8" upper headtubes and has a size of IS41. 2/28. 6. It uses cartridge bearings. Features Size: 1-1/8" IS41. 2/28. 6 (36/45) 6. 7/8. 2mm Replacement headset upper from FSAManufacturer part number: 121-0520 | Fsa | Integrated Headset Upper Is-2 | Black | 1-1/8 Is41. 2/28. 6 (36/45) 6. 7/8. 2Mm