There are some common sizes, 1 1/8", 1" and your high grade mtn bikes are way bigger, i measured the outside diameter and mine was an inch and an eigth so i was able to fit a threadless set of a Giant forks and a beafy neck that one of my buddys let me have when we did a side job for him, my suggestion is to take off your neck and measure the outside diameter of the fork stem, then you know exactly what size you will need, Than hit up some local bike shops that resale used items and eventually you will come across a good set!!!