A retention sleeve (150) is placed over the rearward end (134) of the outer conductive shell (120) of a coaxial plug connector (100), providing a rearward stop for retaining the coupling nut (12) on the shell. The retention sleeve can include an inwardly directed flange (158) at its rearward end for retention of an annular solder preform (132) within the cable-receiving bore (136) of the outer conductive shell. The retention sleeve (150) can be of low resistance copper having a thin outer layer (170) of magnetic high resistance metal, defining a self-regulating temperature source when subjected to RF current, to reflow the solder of the preform (132) and thus solder the outer conductive shell (120) to the semirigid outer conductor (82) of the coaxial cable end inserted into the cable-receiving bore (136) providing for automated soldering.