If it feels like it might round off. You will be able to tell by seeing the wrench move but the metal line fitting is not moving and if you remove wrench you will see the sharp corners starting to round. Use a good small vise grip and get it tight on two flat spots and when you go to loosen, do it quick. Not a little pressure at a time, jerk it quick. When it breaks loose, remove the vise grip and use your wrench to remove the rest of the way. When you tighten back in to the new hose fitting you should be able to tighten enough for no leaks but always double check all threaded fittings for leaks when you finish the job.
