A headset is two cups, each with a standard of its own (S.H.I.S.: EC34, ZS44, IS52…), and the frame states both. When a spec sheet names only the brand, the honest answer is "unknown".
- 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.