9 and 10 inch wheel cylinders

I am in the process of renewing the brake system on my son's 69 Dart GT whihc has 9 inch drums so I figured I would upgrade to stainless steel brake hoses but can't find any for 9" drums plenty for 10". So I have to ask are there different tube thread sizes for 9" and 10' wheel cylinders? It doesn't make much sense that the powers that be at Chrysler design would have 2 different line sizes, logically speaking one size line is more cost effect for production purposes heck you don't need to upgrade to a larger size line when you upgrade to disc brakes and good luck getting an answer from the local auto parts store.

Thanks in advance