Your best answer is right here. I usually use a die on the end that I am going to solder on to the fitting, rather than just rough up with sand paper or a file. This gives the male rod end a better surface for solder to hold on to inside the female brass fitting. I usually flux it and tin it after cutting some rough threads with a die. Haven't had one come loose in flight yet. Many of us are using althread and carbon fiber tube to make really strong push rods for the larger airplanes. There are some really good threads in the building sections on many of the techniques used. DO NOT TRUST A ROD YOU HAVE TRIED TO CUT THREADS IN YOURSELF, it will pull out under heavy load. Good luck and follow Kens advice.