I use .025 wire and I USE A 75%/ 25% MIXTURE ARGON/CO2,ALSO MAKE SURE YOU HAVE A GOOD FIT, MOST PROBLEMS , ARE TRYING TO FILL IN LARGE GAPS,TAKE YOUR TIME IN FITTING AND TACK EVERY 1/4 INCH IF YOU HAVE TWO,TRY THIS BELIVE ME WITH PRACTICE YOU WILL DO FINE. OLD NAVY 51............