:p my guess is if you are laying under the car,looking up at the pitman arm then you would be the LARGE NUT UNDER THE PITMAN ARM :p
Just kidding
If you cant find a socket the right size at a hardware store then you'll have to go to an automotive store or tool truck.
pitman arm nuts can be torqued on pretty tight so use a large impact wrench or a long johnson bar to break it loose