Hey all, I'm new here- I'm trying to replace the rear transmission seal on the 2005 mustang v6 automatic (5R55S) and I have to remove the "output shaft flange nut" and I can't find the right size socket ANYWHERE. I know it has to be a d/w 12 point, just not sure what size...

 

Try this link.
http://iihs.net/fsm/?dir=239

It wont give you the size but it will give the tool call out. then you can find it online or at a parts store.