This 200 micron bag is a convenient re-usable pre-filter for coarse items. It preserves the finer mesh used in the final filtration and can be cleaned for multiple uses. It is also useful in colder temperatures: if oil will not flow through the usual filter bag, this one can be used. In that case, greater reliance will be placed on the on-board (spin-on) fuel filter, which will need to be replaced more frequently.