We make five different crown race sizes, and they are labeled by “bearing size” first, and “crown race seat diameter” second. For example, a 52/40 crown race will work with a 52mm bearing and 40mm crown race seat diameter. First, figure out what size bearing your lower headset assembly takes. Then, confirm the crown race seat diameter on your fork. If you’re having trouble accurately determining these numbers, please visit your local bike shop for help, or visit the S.H.I.S page and our “I want to replace the bearing in my Cane Creek headset. What size do I need?” FAQ.