there is a half circle groove at the bottom of the threads that it should fit in. if you have removed it and thought, I will clean it whilst im at it?? then as you clean it, it sometimes stretches a bit, and will never fit again?? how do I know,:lol: but there some rings that are about 1/4" diameter and some slightly smaller ones, which one is correct I am not sure(probably the larger one as have a few)
16Saabs, do I understand you correctly that the O ring goes between the top of the fuel pump and the bottom of the threaded ring with the bottom of the fuel pump module sitting on the top of the fuel tank? If yes, what seals the fuel module to the gas tank? Thanks.