I just bought a new bianchi infinito frameset and have no idea which headset to get. The size would be 1 1/8th inches, but I have no idea what the frame takes. Do I need to buy a threadless headset? Integrated? I'm lost.
A quick check of the Bianchi website tells you that the bike normally comes with an FSA Orbit CE headset. Another google search informs you that the FSA Orbit CE is an integrated, threadless, 1.125" headset.
However, in the event that you can't find this info it is still easy to check:
If there are threads on the top of the fork steerer: if so then threaded, if not then threadless (if the steerer is carbon or aluminium then it is VERY unlikely to be threaded).
The head tube of a frame suited to integrated headsets has special recesses top and bottom to accomodate the bearing cups or the bearings themselves. If the headtube instead has a plain bore at each end then it is suited to standard press fit cups. There are also some frames which have a press fit cup at one end and an integrated cup at the other.