Ugly Moosling
Full Access Member
You're missing the point. The o rings still provide the primary seal, the copper washer compresses and merely holds the cap stationary while allowing the flared lines to maintain their tension.The tension prevents the o-rings from failing prematurely due to a cap getting moved while working on other things around them.
I understand what you're getting at, I just think trying to get just the right amount of tension to compress the washer and seal the flare at the same time is asking a lot. I feel like you would end up with some caps being loose and others being too right to allow the flare to seat. You could always have an assortment of different thickness washers, but to me it seems like too much effort to get the perfect combo.