Locknut size help

[D-600]

I have a 75-80 D600 front d-60 with external drive flanges. I am doing an axle swap but can't seem to find the right size locknut socket. every auto store in town has too small socket. I tried to measure it and I am getting around 3 inches. I need to know the exact size of the nut or the size socket. Any help would be greatly appreciated. Thank-You


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