Bearings are what allow the gears to rotate easily. They are usually made from bronze or brass, and so they in shape into races (or grooves) during the gearbox housing. Synchro rings have teeth on them that mesh Using the teeth about the gears, and so they also have friction https://andersontjudl.laowaiblog.com/33084522/the-definitive-guide-to-filter-gearbox