A tube fitting including a sleeve member having a circumferential collar portion, the circumferential collar portion including a first tapered surface, a first coupling member having a circumferential engagement flange portion configured to couple with the circumferential collar portion of the sleeve member, and a second coupling member that includes a longitudinally extended sealing portion. The longitudinally extended sealing portion includes a second tapered surface that couples with the first tapered surface so as to circumferentially expand the longitudinally extended sealing portion, when the first tapered surface and the second tapered surface are coupled to each other, and form a fluid seal between the second coupling member and the sleeve member.