fuel line fitting leakage

Paula W

I have a leaking fitting on the fuel pump side of the line to the carburetor. (See photo.) We removed and reattached it as part of trouble shooting a starting problem.
Unfortunately, after reattaching the fuel side fitting now leaks. I tried tightening as much as I could but started to strip the nut.
Should it be this hard to tighten?
Did we damage it, hence need to replace the line and fittings?
What is the wrench size? 7/16 came the closest for us, but as not perfect we ended up stripping the nut.

I did this to myself and don't want to do it again if possible.

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