What size socket do I need for oil drain plug? Thanks!

 

Whatever size it takes- Factory was 3/4 or 7/8, many aftermarket ones are 1/2 or 9/16, I have seen 5/8 ones as well.
I usually just use an adjustable. One tool, regardless of bolt size.

Also very easy to find out what size by getting under the truck.

 

mine was 7/8 as was every other EFI 300 i was under...but ya why not go out and try a few wrenches to see.