JReade, to expand on what Jimmuller said, find the diameter of the steerer tube near the middle below the threads. Calipers are needed for an accurate measurement. You should end up with 1", 1 1/8", or 1 1/4". Then measure the diameter where the steerer meets the fork crown, where the crown race will sit. I believe this is standardized on everything except a 1" which has two different crown race diameters. If you have a 1", this measurement is critical since the two different sizes are very close to one another. I can't remember what the two possible measurements are though. For stack height, measure the head tube length and add the stack height. This number should be just longer than the steerer tube length. That's so the top nut doesn't bottom out when tightening. The steerer can be cut down some to make it fit but a large amount might mean having to get more threads cut so the headset can be screwed on far enough. Hope this helps.