A tubing or fitting assembly has an inner tube layer, an outer tube layer, a sleeve, a tip portion, and can have a nut. Each of the nut, sleeve, inner and outer tubing layers, and tip portion have a passageway therethrough, with at least the passageways in the sleeve, tip portion, outer tube layer, and nut adapted to allow the inner tube layer to pass therethrough or extend over the inner layer. The tip portion can be molded over an end portion of the inner tube layer and also over a portion of the sleeve. The ends of the tip portion and inner layer together define a substantially flat surface which can form a seal in a flat-bottomed port of a component such as may be found in any one of a number of components in an analytical instrument system, including for example a liquid chromatography system.