removing coupling nut under the ballcock valve

I assume the coupling nut (bottom outside of tank) will turn the same direction to loosen the ballcock valve as the water supply nut at the bottom of the tank just below the coupling nut ?
With this in mind I've tried to tried to untighten the coupling nut but I was afraid I might strip this plastic nut (perhaps 1/4 thick and not much to grab onto). What is the best tool to remove this coupling nut from under the tank? Special type wrench or just use a hack saw to cut the nut and threads?
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Jim wrote:

You can use a slip-joint pliers but don't squeeze; doing so will squash the nut onto the threads. If all else fails, go ahead and hacksaw thru it.
Jim
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Thank Jim.
For what it's worth to use the correct terminology, I called it a coupling nut but actually I think I should call it a lock down nut (just on the ballcock valve on the bottom of the tank tightened to the tank to hold down/secure the ballcock valve.
I had to use a mini hacksaw tool (just perfect for this job) and cut about 1/3 into the top of the lock down nut (I scraped the tank a little in sawing) and then used a pair of pliers to grab the threaded stem (ball cock valve below the tank) and wiggled it till it just snapped off (sheared off) and then all was solved. I also had to replace the 2 washers that secure the tank to the bowl but that was easy to take out and replace.
Other than the sawing (about 10 minutes using a new mini hacksaw) it wasn't a bad job. I did note that the new lock down nut says to hand tighten but that won't work because it still leaks so I had to use the pliers to tighten it just a bit more till the water leak stopped. Now all is working well.
Again thanks Jim and for the benefit of others here I posted the stuff above.
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