I had this problem myself, and none of the above spindle nut sockets where the answer. my truck is a 96 ford f150 4x4 4.9 with manual hubs. it looked like a socket but it wasnt quite circular on the inside, kinda oblong on one side.

 

Gonna have to find the socket pictured in fordtrucknut's post. I used one similar to the one pictured in Andrew95's post - yep, if you ain't careful, your knuckles will start leaking red and the tangs on the socket will irreparably bend/break.