hello, just wondering, are all steerer tubes the same diameter? I.E a 1.1/8th steerer the same as a 1" one? So is it just the head tubes and headsets that are the different sizes?
Generally you must use the right size parts for the headtube, if you have an 1 1/8" headtube you need to use an 1 1/8 steerer and headset, same with 1" and 1 1/4"
But a smaller diameter steerer can be shimmed out to fit a larger diameter headset though and shims can be used to fit a smaller diameter headset into a larger diameter headtube e.g a 1 1/8 headset can be fitted to a 1 1/4 headtube using shims, also Chris King do devolution headsets which allow fitting an 1 1/8 steerer into a 1 1/4 headtube.
That's probably confusing but it's pretty straightforward, honest