I bought 6AN weld bungs as well, but the 8AN bungs were a better fit for welding to the rail. I am actually going to use 8AN to 6AN reducers for the return lines; my APFR has 6AN inlets. My check valve after the Walbro fuel pump has 8AN fittings, and I will run a 8AN supply line from the check valve to the rail inlet.