You bought a new diff or you just want to know ? I recently bought the alloy differential and its the same diff as the adjustable one. Exept for the shell. If you have the standard alloy diff shell you cant adjust it, only poke things into the hole in the diff housing

Otherwise there is supposed to go some kinda screw through that hole that you adjust from the shell.
http://www.buildersedge.net/fgcat2004/Html/154.htm