A fitting for making a metal-to-metal fluid seal between a first conduit and a second conduit and corresponding first and second fluid passages. The first conduit has a generally spherical-shaped exterior surface, and the second conduit has a generally conical-shaped interior surface for receiving the generally spherical-shaped exterior surface of the first conduit. A nut is engaged with a threaded exterior surface of the second conduit, tightening of the nut on the threaded exterior surface urging the first and second conduits axially together to apply increasing pressure. A ring can be positioned between the nut and the first conduit, the ring providing a lower net coefficient of friction during tightening of the nut compared to direct contact between the nut and first conduit. The ring can be radially spaced from a radially facing interior surface of the nut.