Im going to paint my wheel wells, i'm removing the train and the caliper from the well
do you have any advice to plug the hardline to prevent it to leak any fluid.
I thought about using a brass female plug but i don't know what diameter the thread of the brake line is at this location.
What guys do you suggest?

 

Push and hold the brake pedal down about half way. This will block off the ports in the master. You will get a couple drips out of the tip of the line and that will be it.

Silicone plugs and caps are common and cheap on amazon.

Or fully evacuate all the brake fluid.

 

Why not just leave the soft line on? Two pennies in a pair of Vise Grips to pinch it off, then bag/tape the whole thing.