I have an old Rock Hopper mountain bike, about 15 or 16 years old, that uses a 1” threaded headset which needs replacing. I have found two types of 1” threaded headsets. One has a 26.4 crown race and the other a 27 crown race. How do I determine which one I need, or does it matter? I haven't found any markings on the headset on there now.