My first time ordering replacement tank ends (love the socket like effect of the black delrins), I wasnt sure if the O-rings would be included. So I went ahead and made sure I had ordered O-rings aswell. When the order arrived, woohoo ends already had O-rings installed, Fast forward to today, my mom gets her black ends in, and what do you know, no O-rings. Luckily I had the ones I had ordered before so no down time, but that is what I wanted to make aware. Order some O-rings just incase. As for the product, A+++ . Never have had any problems (cosmetic or leaks). BTW I drop tanks daily skating, never had any major damage besides scuffs!