Hey Joe,
Its a good idea to state what the Make, Model & Year of the vehicle you are asking the question about.
I assumed its a Chevrolet 1955 1st series 3100 1/2 ton truck.
According to the 1929-1957 Master Parts Catalog
Group number 4.680 Hose Assembly, Hydraulic Brake
Hose Hex size is 7/16
Thanks,
