A replacement stem must clamp the handlebar already on the bike and the steerer it sits on. Both diameters are safety-critical; both are cited on every stem page.
- How do I know whether a part in this category fits my bike?
- Every part page lists the standards it requires and its computed verdict on each bike in the fleet, with its confidence and sources. An "unknown" verdict means we do not have the measurement on file — not that it fits.