When I changed the main fuel filter on my car, there was a small o-ring and a brass crush washer provided with it. As I looked at the 27mm hollow bolt that attaches the filter to the housing, I came to the conclusion that these items were not needed for my particular application. This bolt has two black o-rings, which were both larger than the one that was provided and had flat edges (didn't seem hard however as I was able to check with my fingernail), and I saw no crush washers underneath the bolt either. Why do they provide these? It was a Knecht/Mahle filter bought from the guy in WA.

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)