I got them as part of a filter service kit from britishparts UK, which included air filter, oil filter, fuel filter, sump washer and these. I thought that they might be for the fuel filter (which I'm not feeling brave enough to install yet), but I noticed it already had it's own copper washers with it.

Anyone know what the o-rings are supposed to be for?

 

Um.

If your car is an X300 then the fuel filter has o/rings on the inlet and outlet pipes, NOT copper washers that I have ever seen, and I reckon that would be them???.

The early XJ40 had copper washers I think.

 

+1