Metal spin on is probably 1 micron -- this is pretty standard for diesel engines newer than 1970 or so.

The small filter is just a screen to catch the big stuff. It can go anywhere before the lift pump.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!