Does this mean that I can just put an english / ISO headset on this bike? Does do not "go back-and-forth" mean that once an english thread headset has been put on the bike, an Italian threaded one will no longer work, or vice versa?
Here's some more info: The headset currently on the bike is a shimano 105 which I'd guess is at least 10 to 15 years old. I have trouble putting on the top threaded race due to a "lip" on the threads of the fork. There is also no washer between the top race and locknut - is this normal for this brand / type of headset? Is this even an Italian headset currently on the bike?