... ,casting feed frame without "P"504 is the code for wire feed frame we have 21,401,402,404,501,502 ... ,we have V,U,K,Three types,"V"fit to steel wire ,"U"fit to fluxcore wire an "K"fit to aluminium wire0.8 ... ,The feed -roll dimension can change it for your welding wire size. Our standard feed-roll size:0.6/0.8 ...