Can I tell the inner diameter of my 1" head tube without removing the headset? I need to replace my 1&quot; threaded headset, but to my surprise the replacement headset is available for either 30.0mm or 30.2mm inner head tube diameter. Is it possible to tell which one I need without removing the headset cups?
Probably not.
Knowing the manufacturer of your bike gives a clue but not always definitive.
One is the Italian size and more common. The other is Japanese.