The star nut is a part that is set into a non-carbon steerer tube that acts as an anchor to help the top cap bolt create tension and adjust threadless headset for proper tightness. The 1" fits 1" steel and some 1 1/8" aluminum steerer tubes while the 1 1/8" fits 1 1/8" steel and some 1 1/4" aluminum steerer tubes. Return to Top