Need to change a headset on a bike, but no idea what sort of headset it needs. I’m a bit lost in all the standards! Its a 1.125″ straight steerer. There is a sticker on the bottom saying “Oversize Headtube”.
Here are some piccies…

Thank you in advance 🙂

(and yes it needs a clean!)

Hope

You appear to have a 1 1/8″ steerer and an oversize headtube. You need to get some sort of reducing headset to suit. I have the same on my bike and it has an FSA headset. Basically it is a normal headset for a 1 1/2″ tapered fork but with a special oversized crown race to fit on the fork to suit.

I guess from the above post Hope do something similar

Checking CRC website it would appear mine came with a standard tapered headset and probably by the looks of it has the nukeproof reducing crown race fitted like this one

http://www.chainreactioncycles.com/nukeproof-reducer-crown-race/rp-prod92344

That looks like a standard internal / zero stack headset to me.

Ghost (if that’s what it is) is one of the makes listed here CaneCreek
If your model is in there it’ll give you the necessary info…