I’ve a Wilier GTR and need to replace the headset. I am fairly sure its a FSA Orbit C-33 ACB Headset (No.44E), but when i come to the buying options, I have the choice between a 9mm or 15mm top cap. What is the top cap referred to here please?

I’ve looked at the FSA guide here and know it is an integrated type headset. Is it simply the stem cap through which the preload screw goes?

It’s the conical bit that sits below the headset spaceres / stem.

So the diameter is relating to the steerer?

It’s the height of the spacer (the bit with FSA in big bold letters), I didn’t even bother to change it, just kept the old one.

Thanks fellas 🙂