It's my understanding that -6AN is supposed to be 3/8" internal diameter which is .375". Not even sure you can drill that return fitting that big. What you have is barely bigger than 3/16", or -3AN.

Last edited by Supercuda; 11/25/16 02:45 PM.
They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.