Originally Posted by Slash5

Campy spec is IS42. IS41 is Cane Creek. I'd say it is IS41 since it's 41mm and blue seal. Looking at the Argon web site, everything they show is IS41.
From the FSA site: Cane Creek Standard integrated headsets use a 35°x45° angular contact bearing (blue seal), Campagnolo a 45°x45° ACB (yellow seal), and TH a 36°x36° bearing (red seal).

FSA Web Store