The definitions of all the letter codes and acronyms are in the beginning of all the parts manuals
D-D as the post asked above is definitely double-duty in this case.
It’s important to decipher all the codes when you are planning your part hunt trip to the junk yard
Some parts are shared across a vast majority of vehicles so you can pick up a much less worn out part sometimes by looking places no one else does
Like at a D-D truck for instance
-s
