Ref - http://forum.studebakerdriversclub.com/showthread.php?103361-Fuel-Hose


An article in Underhood Service in the August 2015 issue explains the codes: 
SAE 30R6 this hose is designed for low pressure applications such as carburetors or emissions hose, not designed for over 10 or 12 psi., or for 100 to 250 degree transmission fluid, the same for SAE 30 R7. Next we have 

SAE 30R9, designed for high pressure applications like fuel injection and oil, it is formulated for under hood heat. The next type is 

SAE 30 R10 this is designed for intank on the fuel pump module, however it is not to used under hood as it doesn't withstand the under hood heat.