Just curious why you would want to ream a brake line??
After cutting there is generally some swarf or, if using a tubing cutter, the I.D. of the tube is "compressed" a bit into the fluid path through the tube. Reaming the tube I.D. cleans up the swarf and allows the flaring tool to seat properly when doing a flare.
I usually run a drill bit into the end of the tube to clean it up, works well to remove the "compressed" edge also.
I have a couple of the reamers pictured. Once I started using a drill bit I had no need for the reamers.
Mark
a counter sink bit works the same.