Originally Posted by
adlai
I see threaded headsets that say 30.2. 30.2 vs 30.0 seems to me like that would be enough margin to fit it on.
The crown race seat should be 30.0. If you have a caliper you can check that. Use grease, a tube the right size and a hammer but as others have said hold the fork in one hand while you tap (it needs a pretty smart tap) on the tube. A heavier hammer may help.
If it really doesn't want to go on try to figure out which component is the wrong size and just sand it down a little bit. So long as it's on there and square it's all good.