Soundguy, looking at the older filter in those pictures, you might be exactly right if that's the one that came off when the other wouldn't go on.. looks like the bottom part of the flange might still be on the tube, nipple or whatever it's called..
Is it possible that the remains of an entire metal cap is up there?? Or did the old filter have a plastic cap?? Looks like it might have lost its top, so to speak.. Like the metal cap pulled up and out of the hole where the plastic shows a higher level, and the entire little metal piece is still up under there? In that case, the o ring might not be visible at all.. The .05 is the thickness of the old metal cap which is still up there.. no?