Bearings are what enable the gears to rotate efficiently. They are usually made outside of bronze or brass, and so they fit into races (or grooves) while in the gearbox housing. Even so, internal filters are dearer than externals and it is much more difficult to exchange internal filters, when https://donovanjfxog.blogpayz.com/34170375/helping-the-others-realize-the-advantages-of-filter-gearbox