don't expoy them. They'll come off eventully. Threaded coupler are not a good idea either. it can be done but using smooth couplers is a better choice. I just use electrical rosin core solder and elcrical flux. Put some flux on the calble and apply solder to it and let the solder wick into it. then do the same to the coupler. Heat the coupler and slowly push in the cable and your done.
You only need to do this to one end. the other end use a quick connector [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXK098&P=0]screw lock[/link]. cut the cable an inch loger than needed and add some solder to the end to keep it from unraveling and push it through one of these