This synchronizer ring is a component inside the gearbox that matches the rotational speed of the target gear to the shaft before engagement. It sits between the hub and the sliding sleeve on the gear cluster; the ring’s friction cone contacts the gear cone to equalize speed, allowing the dog teeth to engage without grinding. A worn ring loses its friction surface, causing gear clash and difficult shifting. The original manufacturer machines the ring to the same cone angle and surface finish as the original assembly, so the friction coefficient and engagement timing are preserved. On reinstall, inspect the hub splines and replace the retaining circlip if deformed.