diameter of front brake steel tube to front caliper hoses needed

[mytoolman]

Hi there all.  Im replacing the flex brake lines to each front caliper. The steel brake tube line that comes from the proportional valve I believe and treads into the front caliper hose was seized. I had to use a tubing cutter to get the hose off.

Does anyone know the size(diameter) of that steel tube that runs from the caliper hose, inside the frame from where the brake caliper hose joins it back about 4 feet to the middle of the RV where the brake boosters are(I remember that steel line to run to the proportional valve but havent climbed under to verify that recently....

i need to order a roll of tubing to make brake line and dont know its diamer...