Abstract: A quick connect tube coupling is configured for use with unstepped bores in conventional fittings, valves, manifolds and similar devices. The coupling includes a tubular tube support which has structure thereon for positively coupling with a brass sleeve which is utilized to retain the coupling in the bore. The tubular tube support further includes a stepped portion which locates a primary O-ring seal for sealing directly with a tube connected by the coupling and a secondary O-ring seal which seals with the wall of the bore. In accordance with a preferred embodiment, the tube support is molded of plastic and is polygonal in cross-section.