Good question but a lot of R9 marked hose is just junk. Big difference between a carb feed line and a supply hose full of gas 24/7 like the pump supply hose. Hose could very well be like brake fluid or a lot of other things. I know from experience that not all DOT4 brake fluid boils at the same temperature, not by a long shot. ATE vs Mercedes fluid is a good example. Mercedes out performs ATE fluid by a very big margin. Some probably just pass the tests and others pass by a lot. I have been using a lot of hose from industrial suppliers, not so much made for over the counter retail purposes. It seems that kind of product is far too often made to be low priced to attract buyers where industrial suppliers are far more performance oriented.