Bearings are what enable the gears to rotate easily. They are usually built outside of bronze or brass, and so they healthy into races (or grooves) while in the gearbox housing. Synchro rings have enamel on them that mesh with the enamel to the gears, plus they even have friction https://donovanaegex.tinyblogging.com/getting-my-filter-gearbox-to-work-77761292