Bearings are what allow the gears to rotate smoothly. They are typically made from bronze or brass, plus they in good shape into races (or grooves) within the gearbox housing. Fundamentally it is made up of a metallic plate with mesh-form inserts that avoid contaminants from moving into the transmission https://johnnyqzejo.blogars.com/32985102/little-known-facts-about-filter-gearbox