An apparatus comprising a sleeve having a first end, a second end, and a center portion; and a lockring slidable on at least the first end. The second end could be the mirror image of the first end or could be any fitting desired to be attached to a tube section. The first end has a constant radius annular chamber such that the end of a tube section slides easily therein initially. The exterior of the first end of the sleeve has a "REVERSE TAPER" configuration such that the exterior radius of the sleeve is least near the center portion and increases generally outward therefrom to a maximum near the end of the sleeve. When the lockring is forced onto the exterior of the sleeve, the sleeve and tube section are deformed the least amount near the center portion, the amount of deformation than generally increasing outward therefrom to a maximum near the end of the sleeve. In the preferred embodiment, this reverse taper is accomplished by a single exterior rib having an inclined surface running therefrom toward the center portion. In another embodiment, the reverse taper is accomplished by a plurality of externally projecting ribs, the first rib near the end of the sleeve being of the greatest radius, and each successive rib toward the center of the apparatus being of successively smaller radius.