Hi,
These are standard and not metric. This means that it is either a 3/8 wrench or 7/16. If neither of these work either then most likely the nut is rounded off which means you need to try and use brake line wrenches. I attached a picture of these. As you can see they have more contact edges to try and prevent it from rounding off.
If nothing else works, then you will need to use vice grips and just get it loose. Then replace the line or repair it and replace the connection point.
Last resort is to cut the line off and replace it. Clearly this option on leaves you one option to repair it so I would not suggest it unless nothing else works or you just want to replace it since you are already replacing the wheel cylinder.
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Monday, March 15th, 2021 AT 7:42 PM