A tubular stem (S) at one end of a nut cage (NC) is inserted into an opening in a wall and is expanded to connect it to the wall and to coldwork the wall material surrounding the opening for fatigue life enhancement. The nut cage (NC) includes a cage floor region (22) for receiving the central portion (46) of a nut (N). One end portion (48) of the nut base (44) is inserted into a socket (22). A second end portion (50) of the nut base (44) is moved axially into a channel (28). Then a snap ring (SR) is installed and moved to place a closed portion (52) over the nut base end portion (50). The socket (26) and channel (28) restrain the nut base (44) against rotation in the nut cage (NC). The channel (28) and a portion of the snap ring (SR) which closes the channel (28) and the axial boundaries of the socket (26) restrain the nut base (44) from axial movement out from the nut cage (NC).