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Compatibility Any frame that uses IS (Integrated Standard) headsets with 41mm upper and 52mm lower outer bearing diameter. Uppers and lowers sold separately. Enduro stainless steel sealed bearings included on both the upper and lower. IS42 is not compatible with Specialized bikes or bikes using the Campagnolo Hiddenset standard Upper headsets ship with a star nut which can only be used on forks with steel or aluminum steerer tubes. For forks with carbon steerer tubes you will need a compression plug (sold separately). (Never use a star nut on a carbon steerer tube).