The filter is also used in other applications with a different sized center bolt (or none, as the W126 with 603 doesn't use one) or different oil drain plug size. Cheaper to put them both in than to stock and sell two different filters.

you will have to buy the two rubber o-rings for the center bolt separately, change them every other oil change.

Peter

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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!